WO2020253292A1 - 一种量子参量放大器 - Google Patents

一种量子参量放大器 Download PDF

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Publication number
WO2020253292A1
WO2020253292A1 PCT/CN2020/080478 CN2020080478W WO2020253292A1 WO 2020253292 A1 WO2020253292 A1 WO 2020253292A1 CN 2020080478 W CN2020080478 W CN 2020080478W WO 2020253292 A1 WO2020253292 A1 WO 2020253292A1
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Prior art keywords
signal
quantum
amplified
frequency
microwave
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PCT/CN2020/080478
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English (en)
French (fr)
Inventor
孔伟成
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合肥本源量子计算科技有限责任公司
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Priority claimed from CN201910525439.9A external-priority patent/CN110277969A/zh
Priority claimed from CN201920907708.3U external-priority patent/CN209930216U/zh
Priority claimed from CN201910522965.XA external-priority patent/CN110138352A/zh
Priority claimed from CN201910522955.6A external-priority patent/CN110120792A/zh
Priority claimed from CN201920907681.8U external-priority patent/CN209930215U/zh
Priority claimed from CN201920908547.XU external-priority patent/CN210327515U/zh
Application filed by 合肥本源量子计算科技有限责任公司 filed Critical 合肥本源量子计算科技有限责任公司
Priority to US17/057,286 priority Critical patent/US11894818B2/en
Publication of WO2020253292A1 publication Critical patent/WO2020253292A1/zh

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    • H—ELECTRICITY
    • H03—ELECTRONIC CIRCUITRY
    • H03F—AMPLIFIERS
    • H03F7/00—Parametric amplifiers
    • H03F7/02—Parametric amplifiers using variable-inductance element; using variable-permeability element
    • H—ELECTRICITY
    • H03—ELECTRONIC CIRCUITRY
    • H03F—AMPLIFIERS
    • H03F19/00—Amplifiers using superconductivity effects
    • G—PHYSICS
    • G06—COMPUTING; CALCULATING OR COUNTING
    • G06N—COMPUTING ARRANGEMENTS BASED ON SPECIFIC COMPUTATIONAL MODELS
    • G06N10/00—Quantum computing, i.e. information processing based on quantum-mechanical phenomena
    • G—PHYSICS
    • G06—COMPUTING; CALCULATING OR COUNTING
    • G06N—COMPUTING ARRANGEMENTS BASED ON SPECIFIC COMPUTATIONAL MODELS
    • G06N10/00—Quantum computing, i.e. information processing based on quantum-mechanical phenomena
    • G06N10/40—Physical realisations or architectures of quantum processors or components for manipulating qubits, e.g. qubit coupling or qubit control
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01P—WAVEGUIDES; RESONATORS, LINES, OR OTHER DEVICES OF THE WAVEGUIDE TYPE
    • H01P7/00—Resonators of the waveguide type
    • H01P7/06—Cavity resonators
    • H—ELECTRICITY
    • H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
    • H10N—ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
    • H10N60/00—Superconducting devices
    • H10N60/80—Constructional details
    • H10N60/805—Constructional details for Josephson-effect devices

Definitions

  • the invention belongs to the field of signal amplifiers, and particularly relates to a quantum parametric amplifier.
  • the qubit reading detection signal is extremely weak.
  • the qubit reading detection signal is usually in the 4-8GHz frequency band, and the power is as low as -140dBm or even below -150dBm.
  • the power of -150dBm to -140dBm corresponds to about 1-10 photons inside the detector.
  • Such a weak detection signal will pass through the detector again. After the spread, there will be additional losses. Therefore, one of the core problems that need to be solved in the application of quantum chips is how to extract effective quantum state information from such a weak qubit read signal.
  • Oscillation amplifier circuit is a commonly used structure in the field of signal amplification and is a key component of many electronic equipment.
  • the oscillation amplifier circuit usually takes the form of an LC oscillation circuit, including interconnected capacitors and inductances. It can be used to generate signals of specific frequencies and also To separate signals of specific frequencies from more complex signals. Because the qubit read signal is a high-frequency signal, its wavelength is very short, and because the traditional LC oscillation circuit uses a large capacitance and inductance device structure, and the energy of the LC oscillation circuit is dispersed in the surrounding space, it dissipates The speed is very fast, so we must use the quantum parametric amplifier applied in the quantum field.
  • the present invention provides a quantum parametric amplifier, so that the frequency of the pump signal of the quantum parametric amplifier in the optimal working mode does not need to be selected as a multiple of the frequency of the signal to be amplified.
  • the quantum parametric amplifier includes a capacitor module, a first microwave resonant cavity, and a superconducting quantum interference device with a tunable inductance that are connected in sequence to form an oscillation amplifier circuit.
  • the superconducting quantum interference device is grounded.
  • the resonant frequency of the first microwave resonant cavity is equal to the frequency of the signal to be amplified
  • the signal to be amplified is coupled from the capacitor module into the oscillation amplifier circuit, and the oscillation amplifier circuit amplifies the signal to be amplified under the action of the pump signal.
  • the quantum parametric amplifier further includes a voltage modulation circuit and/or a second microwave resonant cavity,
  • One end of the voltage modulation circuit is connected to an end of the superconducting quantum interference device close to the first microwave cavity, and the voltage modulation circuit is used to provide a bias voltage for the superconducting quantum interference device.
  • the quantum interference device releases at least one of the idle frequency signals generated in the oscillation amplifier circuit under the action of the bias voltage;
  • One end of the second microwave resonant cavity is connected to an end of the superconducting quantum interference device close to the first microwave resonant cavity, and the resonant frequency of the second microwave resonant cavity is one of those generated by the oscillation amplifier circuit
  • the frequencies of the idle frequency signals are equal.
  • the adjustment of the working mode of the quantum parametric amplifier of the present invention is no longer limited only by the pump signal, but is adjusted by the bias voltage provided by the voltage modulation circuit or/and the resonant frequency of the second microwave cavity and the pump signal.
  • the frequency of the pump signal that makes the quantum parametric amplifier in the best working mode does not need to be selected as a multiple of the frequency of the signal to be amplified.
  • every irrelevant signal generated in the quantum parametric amplifier can be The frequency difference between the signal to be amplified and the signal to be amplified is maintained in the frequency spectrum that can be split by the filter or released, thereby facilitating the subsequent filter to eliminate these irrelevant signals, and improving the fidelity of the quantum parametric amplifier for reading the qubit signal.
  • FIG. 1 is a schematic structural diagram of a quantum parametric amplifier according to Embodiment 1 of the present invention.
  • FIG. 2 is a schematic circuit diagram of a quantum parametric amplifier according to Embodiment 1 of the present invention.
  • FIG. 3 is a schematic structural diagram of a quantum parametric amplifier according to Embodiment 2 of the present invention.
  • FIG. 4 is a schematic circuit diagram of a quantum parametric amplifier according to Embodiment 2 of the present invention.
  • FIG. 5 is a schematic structural diagram of a quantum parametric amplifier according to Embodiment 3 of the present invention.
  • FIG. 6 is a schematic circuit diagram of a quantum parametric amplifier according to Embodiment 3 of the present invention.
  • FIG. 7 is a schematic structural diagram of a quantum parametric amplifier according to Embodiment 4 of the present invention.
  • FIG. 8 is a circuit principle diagram of a quantum parametric amplifier according to Embodiment 4 of the present invention.
  • 100-capacitance module 200-first microwave cavity, 300-superconducting quantum interference device with adjustable inductance, 310-superconducting quantum interferometer, 320-flux modulation circuit, 400-voltage modulation circuit, 500 -Second microwave cavity, 600-filter, 700-circulator, 800-second capacitor module.
  • this embodiment provides a quantum parametric amplifier.
  • the quantum parametric amplifier includes a capacitor module 100, a first microwave resonant cavity 200, and a tunable inductance superconductor that are sequentially connected to form an oscillation amplifier circuit.
  • Quantum interference device 300 Quantum interference device
  • the capacitor module 100, the first microwave cavity 200 and the superconducting quantum interference device 300 are sequentially connected, the superconducting quantum interference device 300 is grounded, and the inductance of the superconducting quantum interference device 300 is adjusted to make the second
  • the resonant frequency of a microwave resonant cavity 200 is equal to the frequency of the signal to be amplified, so that the signal f s to be amplified has the best resonant amplification effect in the first microwave resonant cavity 200.
  • the signal f s to be amplified is coupled into the oscillation amplifying circuit from the capacitor module 100, and the signal f s to be amplified and the pump signal f p perform a nonlinear interaction in the first microwave resonator 200, thereby amplifying the signal to be amplified. Amplify the signal f s . It should be noted that the pump signal f p is also coupled from the capacitor module 100 into the oscillation amplifier circuit.
  • the output signal includes not only the amplified signal, but also various idle frequency signals f i , that is, the oscillation amplifying circuit in the pump signal f p Under the action, the amplified signal f s is amplified, and several idle frequency signals f i are generated.
  • each of the idle frequency signals f i satisfies the following formula:
  • m, n, and l are positive integers
  • f s is the frequency of the signal to be amplified
  • f p is the frequency of the pump signal
  • f i is the frequency of the idle signal.
  • the basic principle of the quantum parametric amplifier is: the inductance generated by the superconducting quantum interference device 300 with tunable inductance is used to form an LC oscillation circuit with a capacitor, thereby constructing a single-mode optical field in the microwave resonant cavity.
  • the weak signal to be amplified and the pump signal enter the device together, and the signal to be amplified is amplified in the microwave cavity, and the whole process is in a superconducting state with almost no dissipation.
  • the superconducting quantum interference device 300 with adjustable inductance includes a superconducting quantum interference device 310 and a magnetic flux modulation circuit 320 connected by mutual inductance coupling, wherein the superconducting quantum interference device is connected in parallel by a Josephson junction
  • the closed-loop device is formed and is connected to the first microwave resonant cavity 200, and the magnetic flux modulation circuit 320 is used to adjust the inductance of the closed-loop device.
  • the Josephson junction is generally composed of two superconductors sandwiched by a very thin barrier layer, such as S (superconductor)-I (semiconductor or insulator)-S (superconductor) structure, referred to as SIS.
  • the superconducting quantum interferometer 310 may be a closed-loop device composed of at least two Josephson junctions in parallel, and the present invention does not limit the number of Josephson junctions.
  • a superconductor can tunnel from one side of a superconductor through a semiconductor or an insulator to a superconductor on the other side, or Josephson effect.
  • the current generated is called Josephson current, which connects multiple Josephson junctions.
  • they form a closed-loop device together they form a Josephson interferometer, or superconducting quantum interferometer.
  • the Josephson junction is a nonlinear inductor, and its inductance has a quantitative relationship with the path current. Therefore, the superconducting quantum interferometer formed by the parallel Josephson structure can form a non-linear inductor with adjustable inductance value, which can then be used to adjust the working performance of the quantum parametric amplifier in the present invention.
  • multi-stage amplifiers are added to the output line of the qubit reading signal to increase the signal strength.
  • the pre-stage amplifier adopts a quantum parametric amplifier.
  • the incidental noise is as low as the level close to the quantum limit, which is the origin of its name.
  • the qubit reading signal that finally leaves the qubit reading detector has 10 effective photons, they will enter the subsequent line and be mixed with thermal noise, electrical noise, etc.
  • the standard thermal noise satisfies the thermodynamic distribution, which can be passed Converted to the number of photons n, where k B is Boltzmann's constant, T is the ambient noise temperature at frequency f, and h is Planck's constant.
  • n is less than 0.1, which is negligible.
  • the receiving system of the qubit reading signal is at room temperature, and n is about 1000. If the qubit reading signal is directly transmitted, then Will be submerged in noise. Therefore, it is necessary to use a parametric amplifier.
  • any amplifier will additionally introduce noise while amplifying the original signal.
  • the amplifier will definitely deteriorate the signal-to-noise ratio. Therefore, the setting of the amplifier should be to raise the gain of the amplifier as much as possible while controlling the noise temperature of the amplifier.
  • the noise temperature also meets Therefore, we can convert the noise temperature into the number of noise photons with frequency f.
  • the signal-to-noise ratio can be described as the ratio of the number of signal photons to the number of noise photons.
  • the best performance of commercial amplifiers is the low-noise amplifier produced by LNF of Sweden, which can amplify signals in the 4-8GHz frequency band with a noise temperature of about 3K.
  • the number of noise photons is about 10
  • the maximum signal-to-noise ratio that can be obtained using a commercial amplifier is about 1.
  • the quantum parameter amplifier has solved the problem of extracting effective quantum state information from such a weak qubit read signal by greatly improving the signal-to-noise ratio, it has brought new problems.
  • the quantum parametric amplifier described in this embodiment further includes a voltage modulation circuit 400, which is connected between the first microwave resonator 200 and the superconducting quantum interference device 300, that is, the voltage modulation circuit 400
  • the superconducting quantum interference device 300 with adjustable inductance is arranged at an end close to the first microwave resonator 200 for providing a bias voltage for the superconducting quantum interference device 300.
  • the superconducting quantum interference device 300 Under the action of the bias voltage provided by the voltage modulation circuit 400, at least one of the idle frequency signals generated in the oscillation amplifier circuit is released.
  • the working principle is as follows: when a bias voltage is applied across the superconducting quantum interference device 300, the current passing through the Josephson junction in the superconducting quantum interference device 300 is an alternating oscillating superconducting current, and its oscillation frequency (or The Josephson frequency) f will be proportional to the bias voltage V, which makes the Josephson junction capable of radiating or absorbing electromagnetic waves, which satisfies the following relationship:
  • h Planck's constant
  • e the electronic charge
  • the superconducting quantum interference device composed of several Josephson junctions in parallel has the ability to absorb electromagnetic waves
  • a bias voltage is applied to the superconducting quantum interference device 300 with adjustable inductance
  • the current Cooper pair on the Josephson junction The energy of absorbing microwave signals is tunneled through the Josephson junction and outflowed.
  • the idle frequency signal generated in the oscillation amplifier circuit will be completely absorbed, which means that the idle frequency signal is released.
  • the microwave resonant cavity must be connected to an external circuit to form a microwave system to work. It must be excited by the microwave signal in the external circuit to establish oscillation in the microwave resonant cavity, and the oscillation in the microwave resonant cavity must be coupled to
  • a capacitor module is usually used to establish a coupling with the microwave resonant cavity.
  • the capacitor module 100 of this embodiment is used to establish a coupling between the outside and the microwave resonant cavity, and couple the signal to be amplified into the first resonant cavity 200 through the established coupling effect.
  • the capacitor module 100 can choose an interdigital capacitor, a distributed capacitor, or a parallel capacitor, and the present invention does not limit the specific form of the capacitor module 100.
  • the signal to be amplified and the pump signal are coupled into the first microwave resonator 200, and the signal to be amplified will be amplified under the action of the pump signal.
  • the inductance of the quantum interferometer 300 makes the working resonance frequency of the first microwave resonator 200 consistent with the frequency of the signal to be amplified, so that the signal to be amplified has the best resonant amplification effect in the first microwave resonator 200.
  • the output signal includes not only amplified signals, but also pump signals, half-frequency pump signals, frequency-multiplied pump signals, and various idle frequency signals.
  • each output idle frequency signal f i also has a filter split from the signal f s to be amplified.
  • the quantum parametric amplifier of this embodiment works, various parameters need to be designed, including the selection of the bias voltage and the frequency of the pump signal.
  • One of the final goals of the present invention is to make the output irrelevant signal None of the idle frequency signals will cause interference to the signal to be amplified, which means that they can be split by the filter.
  • the frequency of the signal to be amplified is 4GHz
  • one of the idle frequency signals can be designed first 2GHz
  • the generated frequency signal f i are amplified signal f s to be kept constant frequency difference, then the other, thereby generating the busy signal frequency f i is not
  • the signal to be amplified f s causes interference.
  • the traditional quantum parametric amplifier also has another problem.
  • the quantum state information of each qubit is carried by an independent signal, and its frequency is similar to other quantum signals.
  • the frequency of the signal carried by the quantum state information of the bit is different.
  • Reading multiple qubits at the same time means that there are multiple signals to be amplified that carry information at the same time, which need to pass through a quantum parameter amplifier.
  • Each of them will produce a large number of irrelevant signals while getting the amplification effect, and at least one of them is close to the signal to be amplified.
  • an irrelevant signal generated by a certain signal to be amplified is likely to be additionally close to the frequency of another signal to be amplified.
  • the frequency of the signal to be amplified f s input to the traditional quantum parametric amplifier is 6.4 GHz and 6.58 GHz (the distance between 0.18 GHz, the filter can be split), the frequency of the traditional quantum parametric amplifier pump signal f p It can be designed to be 6.5GHz, which corresponds to the four-wave mixing mode.
  • the pump signal f p is designed to be 5.2GHz and the corresponding bias voltage. It is known that according to the mixing of the 5.2GHz pump signal f p with the amplified signal f s signal of 6.4GHz and 6.58GHz, all the idle frequency signals f i obtained are maintained with the amplified signal f s of 6.4GHz and 6.58Ghz Splittable frequency difference.
  • the adjustment of the working mode of the quantum parametric amplifier described in this embodiment is no longer limited only by the pump signal, but is adjusted by the bias voltage provided by the voltage modulation circuit 400 and the pump signal together.
  • each irrelevant signal generated in the quantum parametric amplifier can maintain a frequency difference that can be split by the filter on the spectrum of the signal to be amplified, thereby eliminating These irrelevant signals improve the fidelity of the quantum parametric amplifier for reading the qubit signal.
  • the pump signal used to amplify the signal to be amplified may also be coupled from the magnetic flux modulation circuit 320 into the oscillation amplifying circuit.
  • the magnetic flux modulation circuit 320 includes a magnetic flux modulation line and a current device connected in sequence, the current device is used to generate a bias current; the magnetic flux modulation line is used to transmit the bias current, and the bias current
  • the set current is used to adjust the inductance of the superconducting quantum interferometer 310.
  • different magnitudes of bias currents produce different magnitudes of magnetic fields, so the magnetic flux passing through the superconducting quantum interferometer will also change with the magnitude of the bias current, and the magnetic flux of the superconducting quantum interferometer will change, and then the superconducting The inductance of the quantum interferometer changes accordingly.
  • the current device for generating the bias current may be a current source, or a voltage source and a resistor connected in sequence that can provide the bias current.
  • the present invention does not add to the specific form of the current source. limit.
  • the quantum parametric amplifier is further provided with a filter 600 at the output end of the oscillation amplifier circuit.
  • irrelevant signals mainly refer to pump signals, half-frequency pump signals, double-frequency pump signals, and various idle frequency signals.
  • the first microwave resonator 200 described in this embodiment is a reflective microwave resonator.
  • the length of the reflection type microwave resonator is (2k+1) times the length of a quarter of the wavelength of the signal to be amplified, where k is an integer ⁇ 0, and the frequency is equal to the signal to be amplified.
  • the frequency signal can form a spatial standing wave structure in the coplanar waveguide microwave cavity.
  • the length of the reflective microwave resonator is a quarter of the wavelength of the signal to be amplified.
  • the electric field distribution of the two ports of the coplanar waveguide microwave resonator that is one-fourth (2k+1) times the wavelength of the signal to be amplified is a node, that is, the electric field intensity distribution is the weakest
  • the other port is the antinode, that is, the place where the electric field intensity distribution is the strongest.
  • the port with the strongest electric field intensity distribution has the strongest electromagnetic signal coupling transmission capability.
  • the signal to be amplified enters or leaves from the same port of the reflective microwave resonator, that is, the antinode.
  • a coplanar waveguide microwave resonator with a length of a quarter of the wavelength of the signal to be amplified has the strongest electric field intensity distribution at the end close to the capacitor module 100, and the weakest electric field intensity distribution is located close to the ultrasonic wave.
  • the output signal will be output from the strongest electric field intensity distribution, that is, the end close to the capacitor module 100.
  • the voltage modulation circuit 400 is arranged at the end of the superconducting quantum interference device 300 close to the first microwave cavity 200, that is, the voltage modulation circuit 400 is connected to the weakest electric field of the reflective microwave cavity.
  • the DC bias voltage output by the modulation circuit 400 hardly affects the microwave signal in the reflective microwave resonator.
  • a coplanar waveguide is three parallel metal thin film conduction band layers prepared on the surface of a dielectric layer.
  • the conduction band layer at the center is used to transmit microwave signals, and the conduction band layers on both sides are connected
  • the biggest difference from the general circuit is that the coplanar waveguide is a distributed circuit element, and its capacitance/inductance/immittance/impedance is evenly distributed along the signal propagation direction of the coplanar waveguide.
  • the impedance of the waveguide is equal everywhere, so there is no signal reflection, the signal can pass almost losslessly; in addition, the coplanar waveguide has no cutoff frequency, and common lumped circuits have a cutoff frequency.
  • microwave signals in most frequency bands can be transmitted unimpeded, so it is also called transmission line, that is, coplanar waveguide transmission line.
  • transmission line that is, coplanar waveguide transmission line.
  • the magnetic flux modulation line for transmitting the bias current may also use a coplanar waveguide transmission line.
  • the quantum parametric amplifier further includes a circulator 700, the circulator 700 is arranged at an end of the capacitor module 100 away from the reflective microwave resonator, and the filter 600 is arranged at the signal output end of the circulator 700, that is, the signal of the circulator 700
  • the output terminal is the output terminal of the oscillation amplifier circuit.
  • the basic technical solution of this embodiment is the same as that of Embodiment 1.
  • the quantum parametric amplifier described in this embodiment further includes a second microwave resonant cavity 500.
  • the microwave resonant cavity 500 is arranged at one end of the superconducting quantum interference device 300 close to the first microwave resonant cavity 200, and the resonant frequency of the second microwave resonant cavity 500 is the same as one of those produced by the oscillation amplifier circuit.
  • the frequencies of the idle signals are equal.
  • the working frequency of the first microwave cavity 200 is equal to the frequency of the signal to be amplified, so that the signal to be amplified is resonantly amplified in the first microwave cavity 200 the best.
  • the signal f s to be amplified is coupled from the capacitor module 100 into the oscillation amplifying circuit, and the signal f s to be amplified and the pump signal f p perform a nonlinear interaction in the first microwave resonator 200, thereby amplifying the signal to be amplified. Amplify the signal f s .
  • the pump signal f p is also coupled from the capacitor module 100 into the oscillation amplifier circuit.
  • the output signal includes not only the amplified signal, but also various idle frequency signals f i , that is, the oscillating amplifier circuit is under the action of the pump signal
  • the amplified signal f s is amplified, and several kinds of idle frequency signals f i are generated.
  • each of the idle frequency signals f i satisfies the following formula:
  • m, n, and l are positive integers
  • f s is the frequency of the signal to be amplified
  • f p is the frequency of the pump signal
  • f i is the frequency of the idle signal.
  • the quantum parametric amplifier in this embodiment is equipped with the second microwave resonator 500, so that part of the energy of the pump signal can be converted into an idle frequency signal equal to the resonant frequency of the second microwave resonator 500.
  • the resonant frequency of the second microwave resonator 500 of the second microwave resonator 500, and then the pump signal is selected by the resonant frequency of the second microwave resonator 500, so that the quantum parametric amplifier can generate a resonant frequency equal to the resonant frequency of the second microwave resonator 500
  • An idle frequency signal is released.
  • the bias voltage applied by the voltage modulation circuit 400 makes the frequency of the idle frequency signal released by the superconducting quantum interference device 300 with adjustable inductance equal to the resonant frequency of the second microwave resonant cavity 500,
  • the idle frequency signal flows out through the second microwave cavity 500 and the superconducting quantum interference device 300 to ground, which optimizes the effect of the idle frequency signal release.
  • the end of the second microwave resonant cavity 500 far away from the first microwave resonant cavity 200 can also be grounded, so that the idle frequency signal can also flow out through the ground.
  • the pump signal frequency f p that makes the quantum parametric amplifier in the best working mode does not need to be selected as the frequency multiple of the signal to be amplified f s .
  • each idle frequency signal fi output also has a frequency difference that can be split by the filter from the signal fs to be amplified, that is, all other than the released idle frequency signal Irrelevant signals can maintain a frequency difference with the signal to be amplified in the frequency spectrum that can be split by a filter, thereby eliminating these irrelevant signals and improving the fidelity of the quantum parametric amplifier for reading the qubit signal.
  • this embodiment provides a quantum parametric amplifier.
  • the quantum parametric amplifier includes a capacitor module 100, a first microwave resonant cavity 200, and a tunable inductance superconductor that are sequentially connected to form an oscillation amplifier circuit.
  • Quantum interference device 300 Quantum interference device 300. Wherein, the capacitor module 100, the first microwave cavity 200 and the superconducting quantum interference device 300 are sequentially connected, the superconducting quantum interference device 300 is grounded, and the inductance of the superconducting quantum interference device 300 is adjusted to make the second
  • the resonant frequency of a microwave resonator 200 is equal to the frequency of the signal to be amplified, so that the signal to be amplified has the best resonant amplification effect in the first microwave resonator 200.
  • the signal to be amplified is coupled into the oscillating amplifying circuit from the capacitor module 100, and the signal to be amplified f s and the pump signal f p perform nonlinear interaction in the first microwave resonator 200, thereby amplifying the signal to be amplified f s .
  • the pump signal f p may also be coupled from the capacitor module 100 into the oscillation amplifier circuit.
  • the output signal includes not only the amplified signal, but also various idle frequency signals f i , that is, the oscillating amplifier circuit is under the action of the pump signal
  • the amplified signal f s is amplified, and several kinds of idle frequency signals f i are generated.
  • each of the idle frequency signals f i satisfies the following formula:
  • m, n, and l are positive integers
  • f s is the frequency of the signal to be amplified
  • f p is the frequency of the pump signal
  • f i is the frequency of the idle signal.
  • the quantum parametric amplifier of this embodiment further includes a second microwave resonant cavity 500, and the second microwave resonant cavity 500 is arranged at an end of the superconducting quantum interference device 300 with adjustable inductance close to the first microwave resonant cavity 200,
  • the resonant frequency of the second microwave resonant cavity 500 is equal to the frequency of one of the idle frequency signals generated by the oscillation amplifying circuit, so that the resonant frequency of the oscillation amplifying circuit is equal to the resonant frequency of the second microwave resonant cavity 500 An idle frequency signal is released.
  • the microwave resonant cavity must be connected with an external circuit to form a microwave system to work. It must be excited by the microwave signal in the external circuit to establish oscillation in the cavity, and the oscillation in the cavity must be coupled to the external load.
  • a capacitor module is used to establish a coupling with the microwave resonant cavity.
  • the capacitor module 100 in this embodiment is used to establish a coupling between the outside and the microwave resonant cavity, and couple the signal to be amplified into the first resonant cavity 200 through the established coupling effect.
  • the capacitor module 100 can select interdigital capacitors, distributed capacitors or parallel capacitors.
  • Interdigital capacitors, distributed capacitors and parallel plate capacitors of the same size have a capacitance value difference of several orders of magnitude.
  • the quantum parametric amplifier in this embodiment is equipped with the second microwave resonator 500, so that part of the energy of the pump signal can be converted into an idle frequency signal equal to the resonant frequency of the second microwave resonator 500.
  • the pump signal frequency f p that makes the quantum parametric amplifier in the best working mode does not need to be selected as the frequency multiple of the signal to be amplified f s , when the selected pump signal f p and the frequency of the signal to be amplified f s can be filtered
  • each idle frequency signal fi output also has a frequency difference that can be split by the filter from the signal fs to be amplified, that is, all other than the released idle frequency signal is irrelevant
  • Both the signal and the signal to be amplified can maintain a frequency difference that can be split by the filter on the spectrum, thereby eliminating these irrelevant signals and improving the fidelity of the quantum parametric amplifier for reading the qubit signal.
  • the quantum parametric amplifier of the present invention works, various parameters need to be designed.
  • One of the ultimate goals of the present invention is to make the idle frequency signal in the output irrelevant signal not interfere with the amplified signal, that is, They can be split by filters.
  • the frequency of the signal to be amplified is 4 GHz
  • one of the idle frequency signals can be designed to be 2 GHz
  • the second microwave resonant cavity 300 can be determined according to the idle frequency signal.
  • Table 2 shows that when the frequency of the signal to be amplified is 4GHz and the frequency of the pump signal is 6GHz, the 8 kinds of idle frequency signals f i that are closest to the frequency of the signal to be amplified f s are generated.
  • the generated frequency signal f i are amplified signal f s to be kept constant frequency difference, then the other, thereby generating the busy signal frequency f i is not
  • the signal to be amplified f s causes interference.
  • the traditional quantum parametric amplifier also has another problem.
  • the quantum state information of each qubit is carried by an independent signal, and its frequency is similar to other quantum signals.
  • the frequency of the signal carried by the quantum state information of the bit is different.
  • Reading multiple qubits at the same time means that there are multiple signals to be amplified that carry information at the same time, which need to pass through a quantum parameter amplifier.
  • Each of them will generate a large number of irrelevant signals while getting the amplification effect, and at least one of them is close to the signal to be amplified.
  • an irrelevant signal generated by a certain signal to be amplified is likely to be additionally close to the frequency of another signal to be amplified.
  • the frequency of the signal to be amplified f s input to the traditional quantum parametric amplifier is 6.4 GHz and 6.58 GHz (the distance between 0.18 GHz, the filter can be split), the frequency of the traditional quantum parametric amplifier pump signal f p It can be designed to be 6.5GHz, which corresponds to the four-wave mixing mode.
  • the resonant frequency f 2 of the second microwave resonator 300 is determined to be 4 GHz according to the idle frequency signal, and according to the 4 GHz signal and 6.4 GHz
  • the amplified signal f s is designed to be 5.2 GHz.
  • the pump signal f p is designed to be 5.2 GHz. It can be known that the 5.2 GHz pump signal f p is mixed with the amplified signal f s signal of 6.4 GHz and 6.58 GHz, and all idle frequencies are obtained
  • the signal f i maintains a separable frequency difference with the amplified signal f s of 6.4 GHz and 6.58 Ghz.
  • the adjustment of the working mode of the quantum parametric amplifier described in this embodiment is no longer limited only by the pump signal, but is adjusted by the resonance frequency of the second microwave cavity 500 and the pump signal together.
  • Can make part of the energy of the pump signal can be converted into an idle frequency signal equal to the resonant frequency of the second microwave resonant cavity 500.
  • a suitable resonant frequency of the second microwave resonant cavity is selected, it passes through the second microwave resonant cavity.
  • the resonant frequency of the microwave resonator 500 is used to select the pump signal, so that an idle frequency signal equal to the resonant frequency of the second microwave resonator 500 can be released in the quantum parametric amplifier, except for the released idle frequency signal. All other irrelevant signals can be separated from the signal to be amplified in the spectrum at a distance that can be split by the filter, thereby eliminating these irrelevant signals and improving the fidelity of the quantum parametric amplifier for reading the qubit signal.
  • the superconducting quantum interference device 300 described in this embodiment includes a superconducting quantum interferometer 310 and a magnetic flux modulation circuit 320 connected by mutual inductance coupling; the superconducting quantum interference device 310 is a closed loop composed of several Josephson junctions in parallel. The device; the magnetic flux modulation circuit 320 is used to adjust the magnetic flux of the closed loop device, thereby adjusting the inductance of the closed loop device, thereby adjusting the inductance of the superconducting quantum interferometer 310.
  • the superconducting quantum interferometer 310 is connected to the first microwave resonator 200, and the magnetic flux modulation circuit 320 is connected to the superconducting quantum interferometer 310 by mutual inductance coupling.
  • the superconducting quantum interferometer 310 used in this embodiment may be a closed loop device composed of two Josephson junctions in parallel, and the present invention does not limit the number of Josephson junctions.
  • the pump signal used to amplify the signal to be amplified may also be coupled from the magnetic flux modulation circuit 320 into the oscillation amplifying circuit.
  • the magnetic flux modulation circuit 320 includes a magnetic flux modulation line and a current device connected in sequence, the current device is used to generate a bias current; the magnetic flux modulation line is used to transmit the bias current, and the bias current
  • the set current is used to adjust the inductance of the superconducting quantum interferometer 310.
  • different magnitudes of bias currents produce different magnitudes of magnetic fields, so the magnetic flux passing through the superconducting quantum interferometer will also change with the magnitude of the bias current, and the magnetic flux of the superconducting quantum interferometer will change, and then the superconducting The inductance of the quantum interferometer changes accordingly.
  • the current device for generating the bias current may be a current source, or a voltage source and a resistor connected in sequence that can provide the bias current.
  • the present invention does not add to the specific form of the current source. limit.
  • the quantum parametric amplifier is further provided with a filter 600 at the output end of the oscillation amplifier circuit.
  • irrelevant signals mainly refer to pump signals, half-frequency pump signals, double-frequency pump signals, and various idle frequency signals.
  • the first microwave resonator 200 described in this embodiment is a reflective microwave resonator.
  • the reflective microwave resonator that is, the coplanar waveguide microwave resonator with a quarter (2k+1) times the wavelength of the signal to be amplified
  • the electric field distribution of the two ports is that one port is the node, that is, the electric field intensity distribution is the most In the weak place, the other port is the antinode, that is, the place where the electric field intensity distribution is the strongest.
  • the port with the strongest electric field intensity distribution has the strongest electromagnetic signal coupling transmission capability.
  • the signal to be amplified enters or leaves from the same port of the reflective microwave resonator, that is, the antinode.
  • a coplanar waveguide microwave resonator with a length of a quarter of the wavelength of the signal to be amplified has the strongest electric field, that is, the antinode is located at one end close to the capacitor module 100, and the weakest electric field is the node. It is located at the end close to the superconducting quantum interference device 300, and the output signal will be output from the end close to the strongest signal coupling that is close to the capacitor module 100.
  • coplanar waveguide described in this embodiment is the same as the other embodiments described above, and the magnetic flux modulation line used to transmit the bias current may also use a coplanar waveguide transmission line, which will not be repeated here.
  • the quantum parametric amplifier further includes The circulator 700 is arranged at an end of the capacitor module 100 away from the reflective microwave resonator, and the filter 600 is arranged at the signal output end of the circulator 700, that is, the circulator 700
  • the signal output terminal is the output terminal of the oscillation amplifier circuit.
  • this embodiment provides a quantum parametric amplifier.
  • the quantum parametric amplifier includes a capacitor module 100, a first microwave resonant cavity 200, and a tunable inductance superconductor that are sequentially connected to form an oscillation amplifier circuit.
  • Quantum interference device 300 wherein, the capacitor module 100, the first microwave cavity 200 and the superconducting quantum interference device 300 are connected in sequence, and the inductance adjustable superconducting quantum interference device 300 is grounded.
  • the resonant frequency of the first microwave resonant cavity 200 is equal to the frequency of the signal to be amplified, so that the resonant amplification effect of the signal to be amplified in the first microwave resonant cavity 200 is the best.
  • the signal to be amplified is coupled into the oscillating amplifying circuit from the capacitor module 100, and the signal to be amplified f s and the pump signal f p perform nonlinear interaction in the first microwave resonator 200, thereby amplifying the signal to be amplified f s .
  • the pump signal f p is also coupled from the capacitor module 100 into the oscillation amplifier circuit.
  • the output signal includes not only the amplified signal, but also various idle frequency signals f i , that is, the oscillating amplifier circuit is under the action of the pump signal
  • the amplified signal f s is amplified, and several idle frequency signals f i are generated.
  • each of the idle frequency signals f i satisfies the following formula:
  • m, n, and l are positive integers
  • f s is the frequency of the signal to be amplified
  • f p is the frequency of the pump signal
  • f i is the frequency of the idle signal.
  • the quantum parametric amplifier described in this embodiment further includes a voltage modulation circuit 400, which is connected between the first microwave resonator 200 and the superconducting quantum interference device 300, and is used for adjusting the inductance.
  • the superconducting quantum interference device 300 with adjustable inductance provides a bias voltage, and under the action of the bias voltage provided by the voltage modulation circuit 400, at least one generated in the oscillation amplifier circuit The idle frequency signal is released.
  • the working principle is as follows: When a bias voltage is applied across the superconducting quantum interference device 300, the current passing through the Josephson junction is an alternating oscillating superconducting current, and its oscillation frequency f (or Josephson frequency) will be the same as the
  • the bias voltage V is proportional, which makes the Josephson junction have the ability to radiate or absorb electromagnetic waves, which satisfies the following relationship:
  • h Planck's constant
  • e the electronic charge
  • the superconducting quantum interference device composed of several Josephson junctions in parallel has the ability to absorb electromagnetic waves
  • a bias voltage is applied to the superconducting quantum interference device 300 with adjustable inductance
  • the current Cooper pair on the Josephson junction The energy of absorbing microwave signals is tunneled through the Josephson junction and grounded.
  • the microwave resonant cavity must be connected to an external circuit to form a microwave system to work. It must be excited by the microwave signal in the external circuit to establish an oscillation in the cavity, and the oscillation in the cavity must be coupled to the external load.
  • a capacitor module and The microwave resonant cavity establishes a coupling, and the number and position of the capacitor modules are related to the type of the microwave resonant cavity.
  • the microwave resonant cavity that is, the first microwave resonant cavity 200, is a transmissive microwave resonator, and the transmissive microwave resonant cavity is a coplanar waveguide microwave resonator whose length is half the wavelength of the signal to be amplified Cavity.
  • the strongest electric field intensity distribution of the coplanar waveguide microwave resonant cavity whose length is one half of the wavelength of the signal to be amplified can be set to be located at the two ends of the coplanar waveguide microwave resonator, and the electric field at the middle position is almost zero.
  • a capacitor module needs to be provided, that is, as shown in FIG. 7 and FIG. 8, both ends of the first microwave cavity 200 are provided Capacitor modules, namely the capacitor module 100 and the second capacitor module 800.
  • the two ends of the first microwave resonant cavity 200 are divided into one end connected to the capacitor module 100 and the other end away from the capacitor module 100.
  • the electric field intensity distribution connected to the capacitor module 100 is the strongest.
  • the first electric field intensity distribution is named the strongest point, and the electric field intensity far away from the capacitor module 100 is named the second electric field intensity distribution strongest.
  • the capacitor module 100 is used to couple the signal to be amplified into the first resonant cavity 200 That is, the second capacitor module 800 is used to couple out the amplified signal from the first resonant cavity 200, and it can also be recorded as one end of the second capacitor module 800 away from the transmissive microwave resonant cavity Is the output terminal of the oscillation amplifier circuit.
  • the capacitor module 100 and the second capacitor module 800 can use interdigital capacitors, distributed capacitors, or parallel capacitors, and the present invention does not limit the specific forms of the two.
  • a filter 600 may be provided at the output end of the oscillation amplifier circuit, as shown in FIG. 8 In order to achieve the filtering requirements of the output amplified signal.
  • the voltage modulation circuit 400 connected between the first microwave resonant cavity 200 and the superconducting quantum interference device 300 is connected to the transmissive microwave resonator.
  • the electric field of the microwave resonator is the weakest, the introduction of a DC bias voltage here will not affect the microwaves in the transmission microwave resonator.
  • the signal to be amplified enters the transmissive microwave resonator from the strongest distribution of the first electric field, and is output from the strongest distribution of the second electric field.
  • the input signal to be amplified and the output signal are isolated.
  • the signal to be amplified will be absorbed in the transmissive resonator The weakest place is amplified, thereby increasing the signal amplification gain.
  • the transmissive microwave resonant cavity may be formed by a pair of coplanar waveguide microwave resonant cavities 210 whose length is a quarter of the wavelength of the signal to be amplified in series.
  • the half-wavelength structure additionally ensures that the signal to be amplified can leave the other port of the coplanar waveguide microwave cavity, so we do not need to apply an additional circulator at the port , To separate the signal to be amplified and the signal to be amplified with the opposite propagation direction.
  • the voltage modulation circuit 400 is connected in series with the pair of coplanar waveguide microwave cavity 210.
  • coplanar waveguide described in this embodiment is the same as the other embodiments described above, and the magnetic flux modulation line used to transmit the bias current may also use a coplanar waveguide transmission line. I won't repeat them here.
  • the inductance of the superconducting quantum interference device 300 is adjusted so that the working resonance frequency of the first microwave cavity 200 is consistent with the frequency of the signal to be amplified, so that the signal to be amplified is
  • the resonance amplification effect in the first microwave resonator 200 is the best.
  • the signal to be amplified and the pump signal are coupled into the first microwave resonator 200.
  • the signal to be amplified will be amplified under the action of the pump signal. It is explained that the output signal includes not only the amplified signal, but also the pump signal, the half-frequency pump signal, the frequency doubled pump signal and various idle frequency signals.
  • each output idle frequency signal f i also has a filter split from the signal f s to be amplified. Frequency difference.
  • the quantum parametric amplifier of this embodiment works, various parameters need to be designed, including the selection of the bias voltage and the frequency of the pump signal.
  • One of the final goals of the present invention is to make the output irrelevant signal None of the idle frequency signals will cause interference to the signal to be amplified, which means that they can be split by the filter.
  • the frequency of the signal to be amplified is 4GHz
  • one of the idle frequency signals can be designed first 2GHz
  • the signal to be amplified to produce a frequency f s closest eight kinds idler f i are amplified signal f s to be kept constant frequency difference, then the other idle, thereby generating the pilot signal f i is not
  • the signal to be amplified f s causes interference.
  • the traditional quantum parametric amplifier also has another problem.
  • the quantum state information of each qubit is carried by an independent signal, and its frequency is similar to other quantum signals.
  • the frequency of the signal carried by the quantum state information of the bit is different.
  • Reading multiple qubits at the same time means that there are multiple signals to be amplified that carry information at the same time, which need to pass through a quantum parameter amplifier.
  • Each of them will generate a large number of irrelevant signals while getting the amplification effect, and at least one of them is close to the signal to be amplified.
  • an irrelevant signal generated by a certain signal to be amplified is likely to be additionally close to the frequency of another signal to be amplified.
  • the frequency of the signal to be amplified f s input to the traditional quantum parametric amplifier is 6.4 GHz and 6.58 GHz (the distance between 0.18 GHz, the filter can be split), the frequency of the traditional quantum parametric amplifier pump signal f p It can be designed to be 6.5GHz, which corresponds to the four-wave mixing mode.
  • the quantum parametric amplifier of the present invention when used, by designing an idle frequency signal, such as 4GHz, according to the 4GHz signal and the 6.4GHz amplified signal f s, the pump signal f p is designed to be 5.2GHz and the bias voltage, it can be known that According to the mixing of the 5.2GHz pump signal f p with the 6.4GHz and 6.58GHz amplified signals f s , all the idle frequency signals f i obtained are detachable from the 6.4GHz and 6.58Ghz amplified signals f s Frequency difference of division.
  • the adjustment of the working mode of the quantum parametric amplifier described in this embodiment is no longer limited only by the pump signal, but is adjusted by the bias voltage provided by the voltage modulation circuit 400 and the pump signal together.
  • each irrelevant signal generated in the quantum parametric amplifier can maintain a frequency difference that can be split by the filter on the spectrum of the signal to be amplified, thereby eliminating These irrelevant signals improve the fidelity of the quantum parametric amplifier for reading the qubit signal.
  • the superconducting quantum interference device 300 with adjustable inductance in this embodiment includes a superconducting quantum interferometer 310 and a magnetic flux modulation circuit 320 connected by mutual inductance coupling; the superconducting quantum interference device 310 is composed of several Josephson junctions. A closed-loop device constructed in parallel; the magnetic flux modulation circuit 320 is used to adjust the magnetic flux of the closed-loop device, thereby adjusting the inductance of the closed-loop device, and then adjusting the inductance of the superconducting quantum interferometer 310.
  • the superconducting quantum interferometer 310 is connected to the first microwave resonator 200, and the magnetic flux modulation circuit 320 is connected to the superconducting quantum interferometer 310 by mutual inductance coupling.
  • the superconducting quantum interferometer 310 used in this embodiment may be a closed loop device composed of two Josephson junctions in parallel, and the present invention does not limit the number of Josephson junctions.
  • the pump signal used to amplify the signal to be amplified may also be coupled from the magnetic flux modulation circuit 320 into the oscillation amplifying circuit.
  • the magnetic flux modulation circuit 320 includes a magnetic flux modulation line and a current device connected in sequence, the current device is used to generate a bias current; the magnetic flux modulation line is used to transmit the bias current, and the bias current
  • the set current is used to adjust the inductance of the superconducting quantum interferometer 310.
  • different magnitudes of bias currents produce different magnitudes of magnetic fields, so the magnetic flux passing through the superconducting quantum interferometer will also change with the magnitude of the bias current, and the magnetic flux of the superconducting quantum interferometer will change, and then the superconducting The inductance of the quantum interferometer changes accordingly.
  • the current device for generating the bias current can be a current source, or a voltage source and a resistor connected in sequence that can provide the bias current.
  • the present invention does not limit the specific form of the current source. .
  • the quantum parametric amplifier is further provided with a filter 600 at the output end of the oscillation amplifier circuit.
  • irrelevant signals mainly refer to pump signals, half-frequency pump signals, double-frequency pump signals, and various idle frequency signals.
  • coplanar waveguide described in this embodiment is the same as the other embodiments described above, and the magnetic flux modulation line used to transmit the bias current may also use a coplanar waveguide transmission line, which will not be repeated here.

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Abstract

本发明公开了一种量子参量放大器，量子参量放大器包括依次连接的用于组成振荡放大电路的电容模块、第一微波谐振腔和可调电感的超导量子干涉装置，超导量子干涉装置接地，所述量子参量放大器还包括电压调制电路和/或第二微波谐振腔，电压调制电路的一端与超导量子干涉装置靠近第一微波谐振腔的一端连接；第二微波谐振腔的一端与超导量子干涉装置靠近第一微波谐振腔的一端连接。本发明的量子参量放大器处于最佳工作模式的泵浦信号的频率无需选择为待放大信号频率的倍频。

Description

一种量子参量放大器
本申请要求在2019年06月17日在中国专利局递交的、申请号为“CN201910522955.6”、发明名称为“一种量子参量放大器”的优先权，其全部内容通过引用结合在本申请中。
本申请要求在2019年06月17日在中国专利局递交的、申请号为“CN201910522965.X”、发明名称为“一种量子参量放大器”的优先权，其全部内容通过引用结合在本申请中。
本申请要求在2019年06月17日在中国专利局递交的、申请号为“CN201910525439.9”、发明名称为“一种量子参量放大器”的优先权，其全部内容通过引用结合在本申请中。
本申请要求在2019年06月17日在中国专利局递交的、申请号为“CN201920907681.8”、发明名称为“一种量子参量放大器”的优先权，其全部内容通过引用结合在本申请中。
本申请要求在2019年06月17日在中国专利局递交的、申请号为“CN201920908547.X”、发明名称为“一种量子参量放大器”的优先权，其全部内容通过引用结合在本申请中。
本申请要求在2019年06月17日在中国专利局递交的、申请号为“CN201920907708.3”、发明名称为“一种量子参量放大器”的优先权，其全部内容通过引用结合在本申请中。
技术领域
本发明属于信号放大器领域，特别涉及一种量子参量放大器。
背景技术
在量子计算领域中，为了得到量子芯片的运算结果，我们需要对量子芯片输出的信号即量子比特读取信号进行采集和分析。量子比特读取探测信号极其微弱，以超导量子比特体系为例，量子比特读取探测信号通常在4-8GHz频段，功率低至-140dBm以下，甚至达到-150dBm以下。考虑到量子比特探测信号与量子比特读取探测器的耦合效率，-150dBm到-140dBm的功率对应探测器内部的光子数量大约为1-10个左右，如此微弱的探 测信号，在经过探测器再次传出后，还会额外受到损失。因此，量子芯片的应用，需要解决的核心问题之一是如何从如此微弱的量子比特读取信号中提取出有效的量子态信息。
振荡放大电路是信号放大领域常用的结构，是许多电子设备的关键部件，振荡放大电路通常表现形式为LC振荡电路，包括互相连接的电容和电感，它既可用于产生特定频率的信号，也用于从更复杂的信号中分离出特定频率的信号。由于量子比特读取信号属于高频信号，其波长很短，而由于传统的的LC振荡电路使用的电容电感器件结构尺寸较大、以及LC振荡电路的能量是弥散分布在周围空间中，耗散速度非常快，因此我们必须使用应用于量子领域的量子参量放大器。
现有量子参量放大器基于非线性混频原理工作，为了有效的将量子比特读取信号进行放大，使得量子参量放大器工作在最佳模式需要额外施加频率与待放大信号频率或者其倍频接近的泵浦信号，例如当施加的泵浦信号接近待放大信号频率时对应的是四波混频工作模式，而施加的泵浦信号接近两倍的待放大信号频率时对应的是三波混频工作模式。
当泵浦信号的频率必须选择为接近待放大信号频率的倍频，在放大器输出的信号中存在频率极其接近待放大信号频率的无关信号，这些无关信号由于频率过于接近待放大信号从而很难通过滤波器消除，它们会干扰量子比特读取信号的解调过程，进而导致量子芯片运算结果的解调保真度与解调效率大幅降低。因此，量子参量放大器处于最佳工作模式时，如何使得泵浦信号的频率无需选择为待放大信号频率的倍频，是本领域技术人员亟需解决的问题。
发明内容
针对上述问题，本发明提供一种量子参量放大器，使得量子参量放大器处于最佳工作模式的泵浦信号的频率无需选择为待放大信号频率的倍频。
一种量子参量放大器，量子参量放大器包括依次连接的用于组成振荡放大电路的电容模块、第一微波谐振腔和可调电感的超导量子干涉装置，所述超导量子干涉装置接地，当所述第一微波谐振腔的谐振频率等于待放 大信号的频率时，待放大信号从所述电容模块处耦合进入所述振荡放大电路，所述振荡放大电路在泵浦信号的作用下放大所述待放大信号，并产生闲频信号，其中，通过调节所述超导量子干涉装置的电感，使所述第一微波谐振腔的谐振频率等于待放大信号的频率，
所述量子参量放大器还包括电压调制电路和/或第二微波谐振腔，
所述电压调制电路的一端与所述超导量子干涉装置靠近所述第一微波谐振腔的一端连接，所述电压调制电路用于为所述超导量子干涉装置提供偏置电压，所述超导量子干涉装置在所述偏置电压的作用下将所述振荡放大电路中产生的至少一种所述闲频信号释放；
所述第二微波谐振腔的一端与所述超导量子干涉装置靠近所述第一微波谐振腔的一端连接，所述第二微波谐振腔的谐振频率与所述振荡放大电路产生的其中一种所述闲频信号的频率相等。
本发明所述的量子参量放大器的工作模式调节不再仅仅受制于泵浦信号，而是通过电压调制电路提供的偏置电压或/和第二微波谐振腔的谐振频率和泵浦信号一起调节，使得量子参量放大器处于最佳工作模式的泵浦信号的频率无需选择为待放大信号频率的倍频，当选择合适的泵浦信号时，可以使得量子参量放大器中产生的每一种无关信号均可以与待放大信号在频谱上保持可被滤波器拆分的频差或者被释放，进而方便后级滤波器消除这些无关信号，提高量子参量放大器对量子比特读取信号的读取保真度。
本发明的其它特征和优点将在随后的说明书中阐述，并且，部分地从说明书中变得显而易见，或者通过实施本发明而了解。本发明的目的和其他优点可通过在说明书、权利要求书以及附图中所指出的结构来实现和获得。
附图说明
为了更清楚地说明本发明实施例或现有技术中的技术方案，下面将对实施例或现有技术描述中所需要使用的附图作一简单地介绍，显而易见地，下面描述中的附图是本发明的一些实施例，对于本领域普通技术人员来讲，在不付出创造性劳动的前提下，还可以根据这些附图获得其他的附图。
图1为本发明实施例1所述的一种量子参量放大器的结构示意图；
图2为本发明实施例1所述的一种量子参量放大器的电路原理图；
图3为本发明实施例2所述的一种量子参量放大器的结构示意图；
图4为本发明实施例2所述的一种量子参量放大器的电路原理图；
图5为本发明实施例3所述的一种量子参量放大器的结构示意图；
图6为本发明实施例3所述的一种量子参量放大器的电路原理图；
图7为本发明实施例4所述的一种量子参量放大器的结构示意图；
图8为本发明实施例4所述的一种量子参量放大器的电路原理图。
图中：100-电容模块、200-第一微波谐振腔、300-电感可调的超导量子干涉装置、310-超导量子干涉仪、320-磁通调制电路、400-电压调制电路、500-第二微波谐振腔、600-滤波器、700-环形器、800-第二电容模块。
具体实施方式
为使本发明实施例的目的、技术方案和优点更加清楚，下面将结合本发明实施例中的附图，对本发明实施例中的技术方案进行清楚、完整地说明，显然，所描述的实施例是本发明一部分实施例，而不是全部的实施例。基于本发明中的实施例，本领域普通技术人员在没有做出创造性劳动前提下所获得的所有其他实施例，都属于本发明保护的范围。
实施例1
请参照图1及图2，本实施例提供了一种量子参量放大器，量子参量放大器包括依次连接的用于组成振荡放大电路的电容模块100、第一微波谐振腔200和可调电感的超导量子干涉装置300。其中，所述电容模块100、第一微波谐振腔200及超导量子干涉装置300依次连接，所述超导量子干涉装置300接地，通过调节所述超导量子干涉装置300的电感使所述第一微波谐振腔200的谐振频率等于待放大信号的频率，从而使得待放大信号f s在所述第一微波谐振腔200内谐振放大效果最好。其中，待放大信号f s从所述电容模块100处耦合进入所述振荡放大电路，待放大信号f s和泵浦信号f p在第一微波谐振腔200中进行非线性相互作用，进而放大待放大信号f s。需要说明的是，所述泵浦信号f p也从所述电容模块100处耦合进入所述振荡放大电路。待放大信号f s和泵浦信号f p进行非线性相互作用后，输出信号中不仅包括放大信号，还包括各种闲频信号f i，即：所述振荡放大电路在 泵浦信号f p的作用下放大所述放大信号f s，并产生若干种闲频信号f i。
需要说明的是，根据非线性混频原理，每一种所述闲频信号f i均满足如下公式：
mf s+nf i＝lf p
其中：m、n、l为正整数，f s为待放大信号频率、f p为泵浦信号频率、f i为闲频信号频率，当待放大信号f s和泵浦信号f p确定时，m、n和l取不同的数值，将得到各种闲频信号f i。
需要说明的是，所述量子参量放大器的基本原理为：利用可调电感的超导量子干涉装置300产生的电感，与电容构成LC振荡电路，从而在微波谐振腔中构建一个单模光场，此时微弱的待放大信号和泵浦信号共同进入器件中，在微波谐振腔中待放大信号被放大，同时整个过程都处于超导状态，几乎没有耗散。
其中，需要说明的是，可调电感的超导量子干涉装置300包括互感耦合连接的超导量子干涉仪310和磁通调制电路320，其中，所述超导量子干涉仪是由约瑟夫森结并联构成的闭环装置，且与所述第一微波谐振腔200连接，所述磁通调制电路320用于调节所述闭环装置的电感。其中，约瑟夫森结一般由两块超导体夹以某种很薄的势垒层而构成，例如S(超导体)-I(半导体或绝缘体)-S(超导体)结构，简称SIS。所述超导量子干涉仪310可以为由至少2个约瑟夫森结并联构成的闭环装置，本发明对约瑟夫森结的个数不做限定。在SIS中，超导电子可以从其中一个超导体一侧隧穿过半导体或者绝缘体到达另一侧的超导体，或称约瑟夫森效应，所产生的电流称为约瑟夫森电流，将多个约瑟夫森结连接在一起形成闭环装置时就构成了约瑟夫森干涉仪，或称超导量子干涉仪。可知，约瑟夫森结是一个非线性电感，其电感与通路电流具有定量关系。因此，由并联约瑟夫森结构成的超导量子干涉仪可以构成电感值可调节的非线性电感，进而用于在本发明中实现对量子参量放大器的工作性能的调节。
目前，通过在量子比特读取信号的输出线路中加多级放大器用以提高信号强度，通常，前级的放大器采用量子参量放大器。量子参量放大器工作时，附带的噪声低至接近量子极限的水平，这正是其名称的由来。
假设最终离开量子比特读取探测器的量子比特读取信号具有10个有效光子，它们将进入后续线路中，与热噪声、电噪声等混在一起。其中，标准的热噪声满足热力学分布，可以通过
Figure PCTCN2020080478-appb-000001
转化为光子数n，上式中k B为玻尔兹曼常数，T为频率为f处的环境噪声温度，h为普朗克常数。假设量子芯片处于10mK温度环境，则根据上式，n小于0.1，可忽略不计，但是，量子比特读取信号的接收系统位于室温，n大约为1000，如果量子比特读取信号直接传出来，则会被淹没在噪声中。因此，使用参量放大器是必须的。
任何放大器在放大原始信号的同时，都会额外地引入噪声。我们通常以噪声的等效温度，也就是噪声来衡量，该指标越大，则噪声越差。放大器一定会恶化信噪比，因此，放大器的设置应该是，尽可能地抬高放大器的增益，同时控制放大器的噪声温度。噪声温度同样满足
Figure PCTCN2020080478-appb-000002
因此，我们可以将噪声温度转化为频率为f的噪声光子数。而信噪比可以描述为，信号光子数与噪声光子数的比值。
目前商用的放大器，性能最好的是瑞典LNF公司生产的低噪声放大器，可以放大4-8GHz频段的信号，噪声温度大约3K。以此衡量，噪声光子数约为10，因此使用商用放大器最大可以获得的信噪比大约为1。最好的量子参数放大器可以达到标准量子极限的噪声水平，也就是n＝0.5。通常，n在0.5-2之内波动。因此，使用量子参数放大器可以使得系统的信噪比有5-20倍左右的提升。
尽管量子参数放大器通过大幅提高信噪比的方式，解决了从如此微弱的量子比特读取信号中提取出有效的量子态信息的问题，但是却带来了新的问题。
而本实施例所述的量子参量放大器还包括电压调制电路400，所述电压调制电路400连接于所述第一微波谐振腔200和超导量子干涉装置300之间，即所述电压调制电路400设置在所述电感可调的超导量子干涉装置300靠近所述第一微波谐振腔200的一端，用于为所述超导量子干涉装置300提供偏置电压，所述超导量子干涉装置300在所述电压调制电路400提供的偏置电压的作用下将所述振荡放大电路中产生的至少一种所述闲频信号 释放。
工作原理如下：当在超导量子干涉装置300两端施加偏置电压时，通过所述超导量子干涉装置300中约瑟夫森结的电流是一个交变的振荡超导电流，其振荡频率(或称约瑟夫森频率)f将与该偏置电压V成正比，这使得所述约瑟夫森结具有辐射或吸收电磁波的能力，其满足如下关系式：
2eV＝hf
其中：h为普朗克常数,e是电子电荷。
由于由若干约瑟夫森结并联构成的超导量子干涉装置具有吸收电磁波的能力，当在所述电感可调的超导量子干涉装置300上施加偏置电压时，约瑟夫森结上的电流库伯对将吸收微波信号的能量隧穿通过约瑟夫森结接地流出，当选择合适的偏置电压时，使得关系式2eV＝hf中f等于振荡放大电路产生的其中一种闲频信号的频率时，所述振荡放大电路中产生的该闲频信号将被完全吸收，表现为所述闲频信号被释放。
需要说明的是，微波谐振腔必须与外电路连接组成微波系统才能工作，必须由所述外电路中的微波信号激励在微波谐振腔中建立振荡，而微波谐振腔中的振荡又必须通过耦合才能输出到外界负载上，通常采用电容模块与微波谐振腔建立耦合。本实施例的所述电容模块100即用于建立外部与微波谐振腔的耦合，并将待放大信号通过建立的耦合作用耦合进入所述第一谐振腔200中。在具体实施的时候，电容模块100可选用交指电容、分布式电容或者平行式电容，本发明对于电容模块100的具体形式不做限制。
而本实施例所述的量子参量放大器，待放大信号和泵浦信号耦合进入所述第一微波谐振腔200中，待放大信号将在泵浦信号的作用下进行放大，通过调节所述超导量子干涉仪300的电感，使得所述第一微波谐振腔200的工作谐振频率与待放大信号的频率一致，从而使得待放大信号在所述第一微波谐振腔200内谐振放大效果最好。需要说明的是输出信号中不仅包括放大信号，还包括泵浦信号、半频泵浦信号、倍频泵浦信号以及各种闲频信号。此时施加合适的偏置电压V时，使得相关物理量满足关系式2eV＝hf，其中f等于某一种闲频信号的频率，所述振荡放大电路中产生的该闲频信号将被完全吸收，使得量子参量放大器处于最佳工作模式的泵浦信号 频率f p无需选择为待放大信号f s的倍频。当选择的泵浦信号频率与待放大信号频率具有可被滤波器拆分的频差时，输出的每一种闲频信号f i也都与待放大信号f s具有可被滤波器拆分的距离。
需要说明的是，本实施例所述的量子参量放大器在工作之前，需设计各种参数，包括选择偏置电压大小以及泵浦信号的频率，本发明的最终目的之一是使得输出的无关信号中的闲频信号均不会对待放大信号造成干扰，也即使得它们能够被滤波器拆分，这里提供一种具体示例，当待放大信号频率为4GHz时，首先可以设计其中一种闲频信号为2GHz，通过关系式2eV＝hf计算得出偏置电压，再根据公式mf s+nf i＝lf p计算得出其中一种可能的泵浦信号频率，例如，取m、n、l均为1时，选取泵浦信号频率为6GHz，此时，再根据所述待放大信号频率、泵浦信号频率和公式mf s+nf i＝lf p确定其他可能的闲频信号，可以证明，当m，n和l取不同整数值时，得到的闲频信号f i均不会对待放大信号f s造成干扰。表1给出了当待放大信号频率为4GHz、泵浦信号频率为6GHz时，产生的与待放大信号f s频率最为接近的8种闲频信号f i。
表1：8种闲频信号f i
m 1 1 1 1 -1 -1 -1 -1
l 1 1 -1 -1 1 1 -1 -1
n 1 -1 1 -1 1 -1 1 -1
f i 2GHz 10GHz -10Ghz -2GHz -2GHz 10GHz -10GHz 2GHz
由表1可知，产生的与待放大信号f s频率最为接近的8种闲频信号f i均与待放大信号f s保持一定频差，那么据此产生的其他闲频信号f i也不会对待放大信号f s造成干扰。
传统的量子参量放大器还存在另一个问题，实际量子芯片工作时，我们需要同时读出大量的量子比特信号，每个量子比特的量子态信息由一个独立的信号携带传出，其频率与其他量子比特的量子态信息携带信号的频率不一样。同时读取多个量子比特意味着，同时有多个携带有信息的待放大信号，需要经过量子参数放大器。它们其中每一个信号在得到放大效果 的同时，都会产生大量的无关信号，并且其中至少有一个无关信号与自身待放大的信号接近。除此之外，某个待放大信号产生的无关信号，很可能额外地与另一个待放大信号的频率接近。
具体的，例如：输入传统的量子参量放大器的待放大信号f s的频率分别为6.4GHz和6.58GHz(相距0.18GHz，滤波器可拆分)，传统的量子参量放大器泵浦信号f p的频率可设计为6.5GHz，对应为四波混频工作模式，那么根据公式mf s+nf i＝lf p，6.4GHz的放大信号f s的其中一个闲频信号f i为6.6GHz，将会影响到6.58GHz信号(相距0.02GHz，很难拆分)。
而当采用本发明的量子参量放大器，通过设计一个闲频信号，例如4GHz，根据4GHz的信号以及6.4GHz的放大信号f s设计泵浦信号f p为5.2GHz和相应的偏置电压，可以得知，根据该5.2GHz的泵浦信号f p分别与6.4GHz和6.58GHz的放大信号f s信号混频作用，得到的所有闲频信号f i均与6.4GHz和6.58Ghz的放大信号f s保持可拆分的频差。
综上，和现有技术相比，本实施例所述的量子参量放大器的工作模式调节不再仅仅受制于泵浦信号，而是通过电压调制电路400提供的偏置电压和泵浦信号一起调节，当选择合适的偏置电压和泵浦信号时，可以使得量子参量放大器中产生的每一种无关信号均可以与待放大信号在频谱上保持可被滤波器拆分的频差，进而可以消除这些无关信号，提高量子参量放大器对量子比特读取信号的读取保真度。
需要说明的是，所述用于放大所述待放大信号的泵浦信号还可以从所述磁通调制电路320处耦合进入所述振荡放大电路。
其中，所述磁通调制电路320包括依次连接的磁通调制线和电流装置，所述电流装置用于产生偏置电流；所述磁通调制线用于传输所述偏置电流，所述偏置电流用于调整所述超导量子干涉仪310的电感。具体的，不同大小的偏置电流产生不同大小的磁场，因而穿过超导量子干涉仪的磁通量也会随着偏置电流的大小发生变化，超导量子干涉仪的磁通量发生变化，进而超导量子干涉仪的电感随之变化。
需要说明的是，所述用于产生偏置电流的电流装置可以是电流源、亦或是依次连接的可以提供所述偏置电流的电压源与电阻，本发明对于电流 源的具体形式不加限制。
具体的，为了滤除输出信号中除了放大信号以外的无关信号，所述量子参量放大器还在振荡放大电路的输出端设有滤波器600。其中，无关信号主要指的是泵浦信号、半频泵浦信号、倍频泵浦信号、以及各种闲频信号。需要说明的是，本实施例所述的第一微波谐振腔200为反射式微波谐振腔。具体的，所述反射式微波谐振腔的长度为待放大信号波长四分之一的(2k+1)倍的共面波导微波谐振腔，其中，k为≥0的整数，频率等于待放大信号频率的信号可在共面波导微波谐振腔中形成空间驻波结构。当k＝0时所述反射式微波谐振腔的长度为待放大信号波长四分之一。
由于反射式微波谐振腔，即待放大信号波长四分之一的(2k+1)倍的共面波导微波谐振腔的两端口的电场的分布为一端口为波节，即电场强度分布最弱的地方，另一端口为波腹，即电场强度分布最强的地方，电场强度分布最强的端口具备最强的电磁信号耦合传输能力，为了降低信号的传输损耗，保证信号的传输，针对反射式微波谐振腔，待放大信号从该反射式微波谐振腔的同一端口，即波腹进入或者离开。
在本实施例中，设置长度为待放大信号波长四分之一的共面波导微波谐振腔的电场强度分布最强处位于靠近电容模块100的一端，电场强度分布最弱处位于靠近所述超导量子干涉装置300的一端，输出信号将从电场强度分布最强处即靠近所述电容模块100的一端输出。
而所述电压调制电路400设置在所述超导量子干涉装置300靠近所述第一微波谐振腔200的一端，即电压调制电路400连接在所述反射式微波谐振腔的电场最弱处，电压调制电路400输出的直流偏置电压对所述反射式微波谐振腔中的微波信号几乎不产生影响。
需要说明的是，在微波领域，共面波导是制备在介质层表面的三条平行的金属薄膜导带层，其中，位于中心的导带层用于传输微波信号，两侧的导带层均连接到地平面，与一般电路最大的区别是，共面波导是一种分布式电路元件，其电容/电感/导抗/阻抗均匀地沿着共面波导信号传播方向分布，共面波导传播的是TEM波，沿着信号传播方向，波导的阻抗处处相等， 因而不存在信号反射，信号能够几乎无损地通过；此外，共面波导没有截止频率，而常见的集总式电路均存在截止频率。对于一段均匀的共面波导来说，绝大部分频段的微波信号都能畅通无阻地传输，因而又叫传输线，即共面波导传输线。当设计的共面波导传输线具有一定长度，并在共面波导传输线的两端分别构建一个电容节点，微波信号遇到节点后反射，在这段传输线中形成谐振。
其中，用于传输所述偏置电流的所述磁通调制线也可使用共面波导传输线。
由于放大后的信号将从反射式微波谐振腔的靠近电容模块100的一侧经由所述电容模块100输出，为了将输入的待放大信号和输出信号进行隔离，所述量子参量放大器还包括环形器700，所述环形器700设置在所述电容模块100远离所述反射式微波谐振腔的一端，所述滤波器600设置在所述环形器700的信号输出端，即所述环形器700的信号输出端为所述振荡放大电路的输出端。
实施例2
请参照图3及图4，本实施例的基本技术方案同实施例1，和实施例1不同的是，本实施例所述的量子参量放大器还包括第二微波谐振腔500，所述第二微波谐振腔500设置在所述超导量子干涉装置300靠近所述第一微波谐振腔200的一端，所述第二微波谐振腔500的谐振频率与所述振荡放大电路产生的其中一种所述闲频信号的频率相等。通过调节所述超导量子干涉装置300的电感，使得所述第一微波谐振腔200的工作频率等于待放大信号的频率，从而使得待放大信号在所述第一微波谐振腔200内谐振放大效果最好。所述待放大信号f s从所述电容模块100处耦合进入所述振荡放大电路，待放大信号f s和泵浦信号f p在第一微波谐振腔200中进行非线性相互作用，进而放大待放大信号f s。需要说明的是，所述泵浦信号f p也从所述电容模块100处耦合进入所述振荡放大电路。待放大信号f s和泵浦信号f p进行非线性相互作用后，输出信号中不仅包括放大信号，还包括各种闲频信号f i，即：所述振荡放大电路在泵浦信号的作用下放大所述放大信号f s，并产生若干种闲频信号f i。
需要说明的是，根据非线性混频原理，每一种所述闲频信号f i均满足如下公式：
mf s+nf i＝lf p
其中：m、n、l为正整数，f s为待放大信号频率、f p为泵浦信号频率、f i为闲频信号频率，当待放大信号f s和泵浦信号f p确定时，m、n和l取不同的数值，将得到各种闲频信号f i。
本实施例所述的量子参量放大器通过设置第二微波谐振腔500，使得泵浦信号的部分能量可以转化为与所述第二微波谐振腔500谐振频率相等的一种闲频信号，当选择合适的第二微波谐振腔500的谐振频率，再通过所述第二微波谐振腔500的谐振频率来选择泵浦信号，可以使得量子参量放大器中产生与所述第二微波谐振腔500谐振频率相等的一种闲频信号释放。
需要说明的是，当电压调制电路400施加的偏置电压使得所述电感可调的超导量子干涉装置300释放的闲频信号的频率等于所述第二微波谐振腔500的谐振频率时，所述闲频信号通过所述第二微波谐振腔500及所述超导量子干涉装置300接地流出，优化了所述闲频信号释放的效果。
其中，所述第二微波谐振腔500远离所述第一微波谐振腔200的一端还可以接地，这样设置，所述闲频信号还可以通过该接地流出。此时，使得量子参量放大器处于最佳工作模式的泵浦信号频率f p无需选择为待放大信号f s的倍频，当选择的泵浦信号f p与待放大信号f s的频率具有可被滤波器拆分的频差时，输出的每一种闲频信号fi也都与待放大信号fs具有可被滤波器拆分的频差，即：除了该被释放的闲频信号的其他所有的无关信号均可以与待放大信号在频谱上保持可被滤波器拆分的频差，进而可以消除这些无关信号，提高量子参量放大器对量子比特读取信号的读取保真度。
实施例3
请参照图5及图6，本实施例提供了一种量子参量放大器，量子参量放大器包括依次连接的用于组成振荡放大电路的电容模块100、第一微波谐振腔200和可调电感的超导量子干涉装置300。其中，所述电容模块100、第一微波谐振腔200及超导量子干涉装置300依次连接，所述超导量子干涉装置300接地，通过调节所述超导量子干涉装置300的电感使所述第一微 波谐振腔200的谐振频率等于待放大信号的频率，从而使得待放大信号在所述第一微波谐振腔200内谐振放大效果最好。所述待放大信号从所述电容模块100处耦合进入所述振荡放大电路，待放大信号f s和泵浦信号f p在第一微波谐振腔200中进行非线性相互作用，进而放大待放大信号f s。需要说明的是，所述泵浦信号f p也可以从所述电容模块100处耦合进入所述振荡放大电路。待放大信号f s和泵浦信号f p进行非线性相互作用后，输出信号中不仅包括放大信号，还包括各种闲频信号f i，即：所述振荡放大电路在泵浦信号的作用下放大所述放大信号f s，并产生若干种闲频信号f i。
需要说明的是，根据非线性混频原理，每一种所述闲频信号f i均满足如下公式：
mf s+nf i＝lf p
其中：m、n、l为正整数，f s为待放大信号频率、f p为泵浦信号频率、f i为闲频信号频率，当待放大信号f s和泵浦信号f p确定时，m、n和l取不同的数值，将得到各种闲频信号f i。
本实施例所述的量子参量放大器还包括第二微波谐振腔500，第二微波谐振腔500设置在所述电感可调的超导量子干涉装置300靠近所述第一微波谐振腔200的一端，所述第二微波谐振腔500的谐振频率与所述振荡放大电路产生的其中一种所述闲频信号的频率相等，可以使得振荡放大电路产生与所述第二微波谐振腔500谐振频率相等的一种闲频信号释放。
需要说明的是，通常微波谐振腔必须与外电路连接组成微波系统才能工作，必须由外电路中的微波信号激励在腔中建立振荡，而腔中的振荡又必须通过耦合才能输出到外界负载上，通常采用电容模块与微波谐振腔建立耦合。本实施例的所述电容模块100即用于建立外部与微波谐振腔的耦合，并将待放大信号通过建立的耦合作用耦合进入所述第一谐振腔200中。在具体实施时，电容模块100可选用交指电容、分布式电容或者平行式电容，相同尺寸大小的交指电容、分布式电容和平行板式电容器件，其电容数值差异几个数量级。在设计量子参量放大器的时候，可根据实际需要，在这三种电容中选择。因此，本发明对于电容模块100的具体形式不做限制。
本实施例所述的量子参量放大器通过设置第二微波谐振腔500，使得泵浦信号的部分能量可以转化为与所述第二微波谐振腔500谐振频率相等的一种闲频信号，当选择合适的第二微波谐振腔500的谐振频率f 2，即f 2＝f i，根据mf s+nf i＝lf p，可得出关系式mf s+nf 2＝lf p，选择合适的泵浦频率f p，即通过所述第二微波谐振腔500的谐振频率来选择泵浦信号，可以使得量子参量放大器中产生与所述第二微波谐振腔500谐振频率相等的一种闲频信号释放。此时使得量子参量放大器处于最佳工作模式的泵浦信号频率f p无需选择为待放大信号f s的倍频，当选择的泵浦信号f p与待放大信号f s的频率具有可被滤波器拆分的频差时，输出的每一种闲频信号fi也都与待放大信号fs具有可被滤波器拆分的频差，即：除了该被释放的闲频信号的其他所有的无关信号均可以与待放大信号在频谱上保持可被滤波器拆分的频差，进而可以消除这些无关信号，提高量子参量放大器对量子比特读取信号的读取保真度。
需要说明的是，本发明量子参量放大器在工作之前，需设计各种参数，本发明的最终目的之一是使得输出的无关信号中的闲频信号均不会对待放大信号造成干扰，也即使得它们能够被滤波器拆分，这里提供一种具体示例，当待放大信号频率为4GHz时，首先可以设计其中一种闲频信号为2GHz，根据该闲频信号确定所述第二微波谐振腔300的谐振频率f 2为2GHz，通过关系式mf s+nf 2＝lf p，令m＝n＝l＝1选择合适的泵浦频率f p为6Ghz，此时，再根据所述待放大信号频率、泵浦信号频率和公式mf s+nf i＝lf p确定其他可能闲频信号，可以证明，当m，n和l取不同数值时，得到的闲频信号f i均不会对待放大信号f s造成干扰。表2给出了当待放大信号频率为4GHz、泵浦信号频率为6GHz时，产生的与待放大信号f s频率最为接近的8种闲频信号f i。
表2：8种闲频信号f i
m 1 1 1 1 -1 -1 -1 -1
l 1 1 -1 -1 1 1 -1 -1
n 1 -1 1 -1 1 -1 1 -1
f i 2GHz 10GHz -10Ghz -2GHz -2GHz 10GHz -10GHz 2GHz
由表2可知，产生的与待放大信号f s频率最为接近的8种闲频信号f i均与待放大信号f s保持一定频差，那么据此产生的其他闲频信号f i也不会对待放大信号f s造成干扰。
传统的量子参量放大器还存在另一个问题，实际量子芯片工作时，我们需要同时读出大量的量子比特信号，每个量子比特的量子态信息由一个独立的信号携带传出，其频率与其他量子比特的量子态信息携带信号的频率不一样。同时读取多个量子比特意味着，同时有多个携带有信息的待放大信号，需要经过量子参数放大器。它们其中每一个信号在得到放大效果的同时，都会产生大量的无关信号，并且其中至少有一个无关信号与自身待放大的信号接近。除此之外，某个待放大信号产生的无关信号，很可能额外地与另一个待放大信号的频率接近。
具体的，例如：输入传统的量子参量放大器的待放大信号f s的频率分别为6.4GHz和6.58GHz(相距0.18GHz，滤波器可拆分)，传统的量子参量放大器泵浦信号f p的频率可设计为6.5GHz，对应为四波混频工作模式，那么根据公式mf s+nf i＝lf p，6.4GHz的放大信号f s的其中一个闲频信号f i为6.6GHz，将会影响到6.58GHz信号(相距0.02GHz，很难拆分)。
而当采用本发明的量子参量放大器，通过设计一个闲频信号，例如4GHz，根据该闲频信号确定所述第二微波谐振腔300的谐振频率f 2为4GHz，根据4GHz的信号以及6.4GHz的放大信号f s设计泵浦信号f p为5.2GHz，可以得知，根据该5.2GHz的泵浦信号f p分别与6.4GHz和6.58GHz的放大信号f s信号混频作用，得到的所有闲频信号f i均与6.4GHz和6.58Ghz的放大信号f s保持可拆分的频差。
综上，和现有技术相比，本实施例所述的量子参量放大器的工作模式调节不再仅仅受制于泵浦信号，而是通过第二微波谐振腔500的谐振频率和泵浦信号一起调节，可以使得泵浦信号的部分能量可以转化为与所述第二微波谐振腔500谐振频率相等的一种闲频信号，当选择合适的第二微波谐振腔的谐振频率，再通过所述第二微波谐振腔500的谐振频率来选择泵 浦信号，可以使得量子参量放大器中产生与所述第二微波谐振腔500谐振频率相等的一种闲频信号释放，而除了该被释放的闲频信号的其他所有的无关信号均可以与待放大信号在频谱上保持可被滤波器拆分的距离，进而可以消除这些无关信号，提高量子参量放大器对量子比特读取信号的读取保真度。
其中，本实施例所述的超导量子干涉装置300包括互感耦合连接的超导量子干涉仪310和磁通调制电路320；所述超导量子干涉仪310为由若干约瑟夫森结并联构成的闭环装置；所述磁通调制电路320用于通过调节所述闭环装置的磁通量，从而调节所述闭环装置的电感，进而调节所述超导量子干涉仪310的电感。其中，所述超导量子干涉仪310与所述第一微波谐振腔200连接，所述磁通调制电路320与所述超导量子干涉仪310互感耦合连接。具体的，本实施例中使用的所述超导量子干涉仪310可以为由2个约瑟夫森结并联构成的闭环装置，本发明对约瑟夫森结的个数不做限定。
需要说明的是，所述用于放大所述待放大信号的泵浦信号还可以从所述磁通调制电路320处耦合进入所述振荡放大电路。
其中，所述磁通调制电路320包括依次连接的磁通调制线和电流装置，所述电流装置用于产生偏置电流；所述磁通调制线用于传输所述偏置电流，所述偏置电流用于调整所述超导量子干涉仪310的电感。具体的，不同大小的偏置电流产生不同大小的磁场，因而穿过超导量子干涉仪的磁通量也会随着偏置电流的大小发生变化，超导量子干涉仪的磁通量发生变化，进而超导量子干涉仪的电感随之变化。
需要说明的是，所述用于产生偏置电流的电流装置可以是电流源、亦或是依次连接的可以提供所述偏置电流的电压源与电阻，本发明对于电流源的具体形式不加限制。
具体的，为了滤除输出信号中除了放大信号以外的无关信号，所述量子参量放大器还在振荡放大电路的输出端设有滤波器600。其中，无关信号主要指的是泵浦信号、半频泵浦信号、倍频泵浦信号、以及各种闲频信号。
需要说明的是，本实施例所述的第一微波谐振腔200为反射式微波谐振腔。具体的，所述反射式微波谐振腔的长度为四分之一待放大信号波长 的(2k+1)倍的共面波导微波谐振腔，其中，k≥0的正整数，当k＝0时，反射式微波谐振腔的长度为待放大信号波长的四分之一。
由于反射式微波谐振腔，即待放大信号波长四分之一的(2k+1)倍的共面波导微波谐振腔，的两端口的电场的分布为一端口为波节，即电场强度分布最弱的地方，另一端口为波腹，即电场强度分布最强的地方，电场强度分布最强的端口具备最强的电磁信号耦合传输能力，为了降低信号的传输损耗，保证信号的传输，针对反射式微波谐振腔，待放大信号从该反射式微波谐振腔的同一端口，即波腹进入或者离开。
在本实施例中，设置长度为待放大信号波长四分之一的共面波导微波谐振腔的电场最强处，即波腹处位于靠近电容模块100的一端，电场最弱处，即波节处位于靠近所述超导量子干涉装置300的一端，输出信号将从靠近信号耦合最强处即靠近所述电容模块100的一端输出。
需要说明的是，本实施例所述的共面波导同上述其它实施例，且用于传输所述偏置电流的所述磁通调制线也可使用共面波导传输线，在此不再赘述。
由于放大后的待放大信号将从反射式微波谐振腔的靠近电容模块100的一侧经由所述电容模块100输出，为了将输入的待放大信号和输出信号进行隔离，所述量子参量放大器还包括环形器700，所述环形器700设置在所述电容模块100远离所述反射式微波谐振腔的一端，所述滤波器600设置在所述环形器700的信号输出端，即所述环形器700的信号输出端为所述振荡放大电路的输出端。
实施例4
请参照图7及图8，本实施例提供了一种量子参量放大器，量子参量放大器包括依次连接的用于组成振荡放大电路的电容模块100、第一微波谐振腔200和可调电感的超导量子干涉装置300。其中，所述电容模块100、第一微波谐振腔200及超导量子干涉装置300依次连接，所述电感可调的超导量子干涉装置300接地，通过调节所述超导量子干涉装置300的电感使所述第一微波谐振腔200的谐振频率等于待放大信号的频率，从而使得待放大信号在所述第一微波谐振腔200内谐振放大效果最好。所述待放大信 号从所述电容模块100处耦合进入所述振荡放大电路，待放大信号f s和泵浦信号f p在第一微波谐振腔200中进行非线性相互作用，进而放大待放大信号f s。需要说明的是，所述泵浦信号f p也从所述电容模块100处耦合进入所述振荡放大电路。待放大信号f s和泵浦信号f p进行非线性相互作用后，输出信号中不仅包括放大信号，还包括各种闲频信号f i，即：所述振荡放大电路在泵浦信号的作用下放大所述放大信号f s，并产生若干种闲频信号f i。
需要说明的是，根据非线性混频原理，每一种所述闲频信号f i均满足如下公式：
mf s+nf i＝lf p
其中：m、n、l为正整数，f s为待放大信号频率、f p为泵浦信号频率、f i为闲频信号频率，当待放大信号f s和泵浦信号f p确定时，m、n和l取不同的数值，将得到各种闲频信号f i。
本实施例所述的量子参量放大器还包括电压调制电路400，所述电压调制电路400连接于所述第一微波谐振腔200和超导量子干涉装置300之间，用于为所述电感可调的超导量子干涉装置300提供偏置电压，所述电感可调的超导量子干涉装置300在所述电压调制电路400提供的偏置电压的作用下将所述振荡放大电路中产生的至少一种所述闲频信号释放。
工作原理如下：当在超导量子干涉装置300两端施加偏置电压时，通过约瑟夫森结的电流是一个交变的振荡超导电流，其振荡频率f(或称约瑟夫森频率)将与该偏置电压V成正比，这使得约瑟夫森结具有辐射或吸收电磁波的能力，其满足如下关系式：
2eV＝hf
其中：h为普朗克常数，e是电子电荷。
由于由若干约瑟夫森结并联构成的超导量子干涉装置具有吸收电磁波的能力，当在所述电感可调的超导量子干涉装置300上施加偏置电压时，约瑟夫森结上的电流库伯对将吸收微波信号的能量隧穿约瑟夫森结接地流出，当选择合适的偏置电压时，使得关系式2eV＝hf中f等于振荡放大电路产生的其中一种闲频信号的频率时，所述振荡放大电路中产生的该闲频信号将被完全吸收，表现为所述闲频信号被释放。
微波谐振腔必须与外电路连接组成微波系统才能工作，必须由外电路中的微波信号激励在腔中建立振荡，而腔中的振荡又必须通过耦合才能输出到外界负载上，通常采用电容模块与微波谐振腔建立耦合，而设置的电容模块的数量和位置与微波谐振腔的类型有关。在本实施例中，微波谐振腔即所述的第一微波谐振腔200为透射式微波谐振腔，所述透射式微波谐振腔为长度为待放大信号波长二分之一的共面波导微波谐振腔。可以设置长度为待放大信号波长二分之一的共面波导微波谐振腔的电场强度分布最强处分别位于该共面波导微波谐振腔的两端，而中间位置的电场几乎为0。此实施例中，为了实现每个电场分布最强处的与外部的耦合连接，均需要设置电容模块，即如图7和如图8所示，在第一微波谐振腔200的两端均设置电容模块，即所述电容模块100和第二电容模块800。
且为了描述方便，记第一微波谐振腔200的两端分为与所述电容模块100相连接的一端和远离所述电容模块100的另一端，与电容模块100连接的电场强度分布最强处命名为第一电场强度分布最强处，远离所述电容模块100的电场强度命名为第二电场强度分布最强处。设置第一电场强度分布最强处为信号耦合进入端，第二电场强度分布最强处为信号耦合输出端，则所述电容模块100用于将待放大信号耦合进入所述第一谐振腔200中，即所述第二电容模块800用于将放大后的信号从所述第一谐振腔200中耦合输出，也可记为所述第二电容模块800远离所述透射式微波谐振腔的一端为所述振荡放大电路的输出端。本实施例中电容模块100和第二电容模块800均可选用交指电容、分布式电容或者平行式电容，本发明对于两者的具体形式不做限制。
另外，在所述第二电容模块800远离所述透射式微波谐振腔的一端为所述振荡放大电路的输出端时，可在所述振荡放大电路的输出端设置滤波器600，如图8所示，以实现输出的放大后的信号的过滤需求。
在本实施例中，当第一微波谐振腔200为透射式微波谐振腔时，连接于所述第一微波谐振腔200和超导量子干涉装置300之间的电压调制电路400连接在所述透射式微波谐振腔的电场最弱处，在此处引入直流偏置电压，不会对所述透射式微波谐振腔中的微波造成影响。待放大信号从第一电场 强度分布最强处进入所述透射式微波谐振腔，从第二电场强度分布最强处输出，输入的待放大信号和输出信号进行了隔离。和采用四分之一波长反射式谐振腔待放大信号在电场最强处进行放大不同，采用二分之一波长共面波导微波谐振腔，待放大信号将在所述透射式谐振腔中信号吸收最弱的地方进行放大，从而提高了信号放大增益。
另外，在具体实施的时候，所述透射式微波谐振腔可以由一对长度为待放大信号波长四分之一的共面波导微波谐振腔210串联形成。与四分之一波长的结构相比，二分之一波长结构额外可以保证，待放大信号可以从共面波导微波谐振腔的另一个端口离开，因此我们不需要在端口处施加额外的环形器，以分离传播方向相反的待放大信号与经放大后的待放大信号。其中，所述电压调制电路400与所述一对共面波导微波谐振腔210的串联处连接。
需要说明的是，本实施例所述的共面波导同上述其它实施例，且用于传输所述偏置电流的所述磁通调制线也可使用共面波导传输线。在此不再赘述。
本实施例所述的量子参量放大器，通过调节所述超导量子干涉装置300的电感，使得所述第一微波谐振腔200的工作谐振频率与待放大信号的频率一致，从而使得待放大信号在所述第一微波谐振腔200内谐振放大效果最好，将待放大信号和泵浦信号耦合进入所述第一微波谐振腔200中，待放大信号将在泵浦信号的作用下进行放大，需要说明的是输出信号中不仅包括放大信号，还包括泵浦信号、半频泵浦信号、倍频泵浦信号以及各种闲频信号。此时施加合适的偏置电压V时，使得相关物理量满足关系式2eV＝hf，其中f等于某一种闲频信号的频率，所述振荡放大电路中产生的该闲频信号将被完全吸收，使得量子参量放大器处于最佳工作模式的泵浦信号频率f p无需选择为待放大信号f s的倍频。当选择的泵浦信号频率与待放大信号频率具有可被滤波器拆分的频差时，输出的每一种闲频信号f i也都与待放大信号f s具有可被滤波器拆分的频差。
需要说明的是，本实施例所述的量子参量放大器在工作之前，需设计各种参数，包括选择偏置电压大小以及泵浦信号的频率，本发明的最终目 的之一是使得输出的无关信号中的闲频信号均不会对待放大信号造成干扰，也即使得它们能够被滤波器拆分，这里提供一种具体示例，当待放大信号频率为4GHz时，首先可以设计其中一种闲频信号为2GHz，通过关系式2eV＝hf计算得出偏置电压，再根据公式mf s+nf i＝lf p计算得出其中一种可能的泵浦信号频率，例如，取m、n、l均为1时，选取泵浦信号频率为6GHz，此时，再根据所述待放大信号频率、泵浦信号频率和公式mf s+nf i＝lf p确定其他可能的闲频信号，可以证明，当m，n和l取不同数值时，得到的闲频信号f i均不会对待放大信号f s造成干扰。表3给出了当待放大信号频率为4GHz、泵浦信号频率为6GHz时，产生的与待放大信号f s频率最为接近的8种闲频信号f i。
表3：8种闲频信号f i
m 1 1 1 1 -1 -1 -1 -1
l 1 1 -1 -1 1 1 -1 -1
n 1 -1 1 -1 1 -1 1 -1
f i 2GHz 10GHz -10Ghz -2GHz -2GHz 10GHz -10GHz 2GHz
由表3可知，产生的与待放大信号f s频率最为接近的8种闲频信号f i均与待放大信号f s保持一定频差，那么据此产生的其他闲频信号f i也不会对待放大信号f s造成干扰。
传统的量子参量放大器还存在另一个问题，实际量子芯片工作时，我们需要同时读出大量的量子比特信号，每个量子比特的量子态信息由一个独立的信号携带传出，其频率与其他量子比特的量子态信息携带信号的频率不一样。同时读取多个量子比特意味着，同时有多个携带有信息的待放大信号，需要经过量子参数放大器。它们其中每一个信号在得到放大效果的同时，都会产生大量的无关信号，并且其中至少有一个无关信号与自身待放大的信号接近。除此之外，某个待放大信号产生的无关信号，很可能额外地与另一个待放大信号的频率接近。
具体的，例如：输入传统的量子参量放大器的待放大信号f s的频率分别为6.4GHz和6.58GHz(相距0.18GHz，滤波器可拆分)，传统的量子参 量放大器泵浦信号f p的频率可设计为6.5GHz，对应为四波混频工作模式，那么根据公式mf s+nf i＝lf p，6.4GHz的放大信号f s的其中一个闲频信号f i为6.6GHz，将会影响到6.58GHz信号(相距0.02GHz，很难拆分)。
而当采用本发明的量子参量放大器，通过设计一个闲频信号，例如4GHz，根据4GHz的信号以及6.4GHz的放大信号f s设计泵浦信号f p为5.2GHz和偏置电压，可以得知，根据该5.2GHz的泵浦信号f p分别与6.4GHz和6.58GHz的放大信号f s信号混频作用，得到的所有闲频信号f i均与6.4GHz和6.58Ghz的放大信号f s保持可拆分的频差。
综上，和现有技术相比，本实施例所述的量子参量放大器的工作模式调节不再仅仅受制于泵浦信号，而是通过电压调制电路400提供的偏置电压和泵浦信号一起调节，当选择合适的偏置电压和泵浦信号时，可以使得量子参量放大器中产生的每一种无关信号均可以与待放大信号在频谱上保持可被滤波器拆分的频差，进而可以消除这些无关信号，提高量子参量放大器对量子比特读取信号的读取保真度。
其中，本实施例所述的电感可调的超导量子干涉装置300包括互感耦合连接的超导量子干涉仪310和磁通调制电路320；所述超导量子干涉仪310为由若干约瑟夫森结并联构成的闭环装置；所述磁通调制电路320用于调节所述闭环装置的磁通量，从而调节所述闭环装置的电感，进而调节所述超导量子干涉仪310的电感。其中，所述超导量子干涉仪310与所述第一微波谐振腔200连接，所述磁通调制电路320与所述超导量子干涉仪310互感耦合连接。具体的，本实施例中使用的所述超导量子干涉仪310可以为由2个约瑟夫森结并联构成的闭环装置，本发明对约瑟夫森结的个数不做限定。
需要说明的是，所述用于放大所述待放大信号的泵浦信号还可以从所述磁通调制电路320处耦合进入所述振荡放大电路。
其中，所述磁通调制电路320包括依次连接的磁通调制线和电流装置，所述电流装置用于产生偏置电流；所述磁通调制线用于传输所述偏置电流，所述偏置电流用于调整所述超导量子干涉仪310的电感。具体的，不同大小的偏置电流产生不同大小的磁场，因而穿过超导量子干涉仪的磁通量也 会随着偏置电流的大小发生变化，超导量子干涉仪的磁通量发生变化，进而超导量子干涉仪的电感随之变化。
需要说明的是，所述用于产生偏置电流的电流装置可以是电流源、抑或是依次连接的可以提供所述偏置电流的电压源与电阻，本发明对于电流源的具体形式不加限制。
具体的，为了滤除输出信号中除了放大信号以外的无关信号，所述量子参量放大器还在振荡放大电路的输出端设有滤波器600。其中，无关信号主要指的是泵浦信号、半频泵浦信号、倍频泵浦信号、以及各种闲频信号。
需要说明的是，本实施例所述的共面波导同上述其它实施例，且用于传输所述偏置电流的所述磁通调制线也可使用共面波导传输线，在此不再赘述。
尽管参照前述实施例对本发明进行了详细的说明，本领域的普通技术人员应当理解：其依然可以对前述各实施例所记载的技术方案进行修改，或者对其中部分技术特征进行等同替换；而这些修改或者替换，并不使相应技术方案的本质脱离本发明各实施例技术方案的精神和范围。

Claims (17)

  1. 一种量子参量放大器，量子参量放大器包括依次连接的用于组成振荡放大电路的电容模块(100)、第一微波谐振腔(200)和可调电感的超导量子干涉装置(300)，所述超导量子干涉装置(300)接地，当所述第一微波谐振腔(200)的谐振频率等于待放大信号的频率时，所述待放大信号从所述电容模块(100)处耦合进入所述振荡放大电路，所述振荡放大电路在泵浦信号的作用下放大所述待放大信号，并产生闲频信号，其中，通过调节所述超导量子干涉装置(300)的电感，使所述第一微波谐振腔(200)的谐振频率等于所述待放大信号的频率，其特征在于，
    所述量子参量放大器还包括电压调制电路(400)和/或第二微波谐振腔(500)，
    所述电压调制电路(400)的一端与所述超导量子干涉装置(300)靠近所述第一微波谐振腔(200)的一端连接，所述电压调制电路(400)用于为所述超导量子干涉装置(300)提供偏置电压，所述超导量子干涉装置(300)在所述偏置电压的作用下将所述振荡放大电路中产生的至少一种所述闲频信号释放；
    所述第二微波谐振腔(500)的一端与所述超导量子干涉装置(300)靠近所述第一微波谐振腔(200)的一端连接，所述第二微波谐振腔(500)的谐振频率与所述振荡放大电路产生的其中一种所述闲频信号的频率相等。
  2. 根据权利要求1所述的量子参量放大器，其特征在于，所述超导量子干涉装置(300)包括互感耦合连接的超导量子干涉仪(310)和磁通调制电路(320)，其中，
    所述超导量子干涉仪(310)为由约瑟夫森结并联构成的闭环装置；
    所述磁通调制电路(320)用于调节所述闭环装置的电感。
  3. 根据权利要求2所述的量子参量放大器，其特征在于，所述磁通调制电路(320)包括依次连接的磁通调制线和电流装置，其中，
    所述电流装置用于产生偏置电流；
    所述磁通调制线用于传输所述偏置电流，所述偏置电流用于调整所述超导量子干涉仪(310)的电感。
  4. 根据权利要求3所述的量子参量放大器，其特征在于，所述磁通调制线为共面波导微带传输线。
  5. 根据权利要求3所述的量子参量放大器，其特征在于，所述电流装置为电流源、或依次连接的用于提供所述偏置电流的电压源与电阻。
  6. 根据权利要求2～5任一项所述的量子参量放大器，其特征在于，所述超导量子干涉仪(310)为由两个约瑟夫森结并联构成的闭环装置。
  7. 根据权利要求2所述的量子参量放大器，其特征在于，所述泵浦信号从所述电容模块(100)和/或所述磁通调制电路(320)耦合进入所述振荡放大电路。
  8. 根据权利要求1所述的量子参量放大器，其特征在于，所述电容模块(100)为交指电容、分布式电容和平行式电容中任一种。
  9. 根据权利要求1所述的量子参量放大器，其特征在于，所述量子参量放大器还包括滤波器(600)，
    所述滤波器(600)与所述振荡放大电路的输出端连接。
  10. 根据权利要求1～5、7～9任一项所述的量子参量放大器，其特征在于，所述第一微波谐振腔(200)为反射式微波谐振腔，所述超导量子干涉装置(300)与所述反射式微波谐振腔的电场强度分布波节处连接。
  11. 根据权利要求10所述的量子参量放大器，其特征在于，所述反射式微波谐振腔为共面波导微波谐振腔，所述共面波导微波谐振腔的长度为所述待放大信号波长的(2k+1)/4，其中，k≥0且k为整数。
  12. 根据权利要求10所述的量子参量放大器，其特征在于，所述量子参量放大器还包括环形器(700)；
    所述环形器(700)与所述电容模块(100)远离所述反射式微波谐振腔的一端相连，用于将所述待放大信号输入所述振荡放大电路，并将所述振荡放大电路产生的放大信号输出。
  13. 根据权利要求1～5、7～9任一项所述的量子参量放大器，其特征在于，所述第一微波谐振腔(200)为透射式微波谐振腔，所述电感可调的超导量子干涉装置(300)与所述透射式微波谐振腔的电场强度分布波节处连接。
  14. 根据权利要求13所述的量子参量放大器，其特征在于，所述透射式微波谐振腔为共面波导微波谐振腔，所述共面波导微波谐振腔的长度为所述待放大信号波长的k/2，其中，所述k≥1，k为整数。
  15. 根据权利要求14所述的量子参量放大器，其特征在于，所述透射式微波谐振腔由一对长度为所述待放大信号波长四分之一的共面波导微波谐振腔(210)串联形成。
  16. 根据权利要求13所述的量子参量放大器，其特征在于，所述量子参量放大器还包括第二电容模块(800)；
    所述第二电容模块(800)与所述透射式微波谐振腔的电场强度分布波腹处连接，用于将所述振荡放大电路产生的放大信号输出。
  17. 根据权利要求1所述的量子参量放大器，其特征在于，所述第二微波谐振腔(500)接地。
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