CN210327515U - Quantum parametric amplifier - Google Patents
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- CN210327515U CN210327515U CN201920908547.XU CN201920908547U CN210327515U CN 210327515 U CN210327515 U CN 210327515U CN 201920908547 U CN201920908547 U CN 201920908547U CN 210327515 U CN210327515 U CN 210327515U
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Abstract
The utility model discloses a quantum parameter amplifier, which comprises a first capacitance module, a transmission type microwave resonant cavity, a second capacitance module and a superconductive quantum interference device of an adjustable inductor, wherein the first capacitance module, the transmission type microwave resonant cavity and the second capacitance module are sequentially connected, one end of the superconductive quantum interference device is connected with the middle part of the transmission type microwave resonant cavity, and the other end is grounded; the oscillation amplifying circuit amplifies a signal to be amplified under the action of a pumping signal and generates a plurality of idle frequency signals, and the oscillation amplifying circuit also comprises a voltage modulation circuit which is arranged at one end of the superconducting quantum interference device close to the transmission type microwave resonant cavity; the superconducting quantum interferometer device can release at least one idler that produces in the oscillation amplification circuit under the effect of the bias voltage that the voltage modulation circuit provided, the utility model discloses the frequency that quantum parametric amplifier is in the pumping signal of best mode need not to select the doubling of frequency for treating the amplified signal frequency.
Description
Technical Field
The utility model belongs to the signal amplifier field, especially a quantum parameter amplifier.
Background
In the field of quantum computing, in order to obtain an operation result of a quantum chip, a signal output by the quantum chip, that is, a qubit read signal, needs to be collected and analyzed, the qubit read signal is usually very weak, a multi-stage amplifier needs to be added to an output line of the qubit read signal to improve signal strength, and a quantum parametric amplifier is usually used as a preceding stage amplifier. When a quantum parametric amplifier is operated, the accompanying noise is as low as a level close to the quantum limit, which is the origin of its name.
The existing quantum parametric amplifier works based on a nonlinear frequency mixing principle, and in order to effectively amplify a qubit read signal, a pumping signal with a frequency close to the frequency of a signal to be amplified or a frequency doubling of the signal needs to be additionally applied when the quantum parametric amplifier works in an optimal mode, for example, a four-wave frequency mixing working mode corresponds to the applied pumping signal close to the signal to be amplified, and a three-wave frequency mixing working mode corresponds to the applied pumping signal close to twice the frequency of the signal to be amplified.
The present problem is that the existing quantum parametric amplifier has to select the frequency of the pump signal as the frequency multiplication of the frequency of the signal to be amplified in the best working mode, and there exist irrelevant signals with the frequency extremely close to the frequency of the signal to be amplified in the output signal, and these irrelevant signals are difficult to be eliminated by the filter because the frequency is too close to the signal to be amplified, and they will interfere the demodulation process of the qubit reading signal, thereby causing the demodulation fidelity and demodulation efficiency of the quantum chip operation result to be greatly reduced.
SUMMERY OF THE UTILITY MODEL
The utility model aims at providing a quantum parametric amplifier to solve not enough among the prior art, make quantum parametric amplifier be in the pumping signal's of best mode frequency need not to select for the doubling of frequency of waiting to amplify the signal frequency.
The utility model adopts the technical scheme as follows:
a quantum parametric amplifier comprises a first capacitor module, a transmission type microwave resonant cavity, a second capacitor module and a superconducting quantum interference device with an adjustable inductor, wherein the first capacitor module, the transmission type microwave resonant cavity, the second capacitor module and the superconducting quantum interference device are used for forming an oscillation amplification circuit; the first capacitor module, the transmission-type microwave resonant cavity and the second capacitor module are sequentially connected, one end of the superconducting quantum interference device of the adjustable inductor is connected to the middle of the transmission-type microwave resonant cavity, and the other end of the superconducting quantum interference device of the adjustable inductor is grounded; and the resonance frequency of the transmission type microwave resonant cavity can be equal to the frequency of a signal to be amplified by adjusting the inductance of the superconducting quantum interference device with the adjustable inductance, wherein: the signal to be amplified is coupled from the first capacitor module and enters the oscillation amplifying circuit, and the oscillation amplifying circuit amplifies the signal to be amplified under the action of a pumping signal and generates a plurality of idle frequency signals;
the quantum parametric amplifier also comprises a voltage modulation circuit;
the voltage modulation circuit is arranged at one end, close to the transmission type microwave resonant cavity, of the superconducting quantum interference device of the adjustable inductor;
the superconducting quantum interferometer device with the adjustable inductance can release at least one idler signal generated in the oscillation amplifying circuit under the action of the bias voltage provided by the voltage modulation circuit.
Furthermore, the superconducting quantum interference device of the adjustable inductor comprises a superconducting quantum interferometer and a magnetic flux modulation circuit which are connected in mutual inductance coupling;
the superconducting quantum interferometer is a closed-loop device formed by connecting a plurality of Josephson junctions in parallel;
the magnetic flux modulation circuit is used for adjusting the magnetic flux of the closed loop device so as to adjust the inductance of the superconducting quantum interferometer.
Further, the superconducting quantum interferometer is a closed-loop device formed by connecting two Josephson junctions in parallel.
Further, the magnetic flux modulation circuit comprises a magnetic flux modulation line and a current device for generating bias current which are connected in sequence;
wherein: the flux modulation lines are used for transmitting the bias current and enabling the bias current to be mutually inductively coupled with the superconducting quantum interferometer.
Further, the magnetic flux modulation line is a coplanar waveguide microstrip transmission line.
Further, the current device is a current source, or a voltage source and a resistor which are connected in sequence and can provide the bias current.
Further, a pumping signal for amplifying the signal to be amplified is coupled into the oscillation amplifying circuit from the first capacitance module or the magnetic flux modulating circuit.
Further, the first capacitor module and the second capacitor module are respectively one of an interdigital capacitor, a distributed capacitor and a parallel capacitor.
Further, the transmission-type microwave resonant cavity is a coplanar waveguide microwave resonant cavity with the length being one half of the wavelength of the signal to be amplified.
Furthermore, the transmission type microwave resonant cavity is formed by connecting a pair of coplanar waveguide microwave resonant cavities with the length of one fourth of the wavelength of the signal to be amplified in series.
Further, the quantum parametric amplifier further comprises a filter;
the filter is arranged at one end, far away from the transmission type microwave resonant cavity, of the second capacitor module.
Compared with the prior art, the utility model provides a quantum parametric amplifier, which comprises a first capacitance module, a transmission microwave resonant cavity, a second capacitance module, a superconductive quantum interference device with adjustable inductance and a voltage modulation circuit, wherein the first capacitance module, the transmission microwave resonant cavity, the second capacitance module and the voltage modulation circuit are used for forming an oscillation amplification circuit; the first capacitor module, the transmission-type microwave resonant cavity and the second capacitor module are sequentially connected, one end of the superconducting quantum interference device of the adjustable inductor is connected to the middle of the transmission-type microwave resonant cavity, the other end of the superconducting quantum interference device of the adjustable inductor is grounded, and the voltage modulation circuit is arranged at one end, close to the transmission-type microwave resonant cavity, of the superconducting quantum interference device of the adjustable inductor; the resonance frequency of the transmission-type microwave resonant cavity is equal to the frequency of the signal to be amplified by adjusting the inductance of the superconducting quantum interference device with the adjustable inductance, so that the signal to be amplified and the pumping signal are subjected to nonlinear interaction in the transmission-type microwave resonant cavity to further amplify the signal to be amplified, and after the signal to be amplified and the pumping signal are subjected to nonlinear interaction, the output signal not only comprises the signal to be amplified, but also comprises various idler frequency signals fiThe frequency of the pump signal for bringing the quantum parametric amplifier into an optimum operating mode when a bias voltage is appliedfpNeed not be selected as the signal f to be amplifiedsSo that each idler f is output when the selected pump signal frequency is at a distance from the signal frequency to be amplified that can be split by a filteriAre also all related to the signal f to be amplifiedsHave the distance that can be by the wave filter split, the utility model discloses a set up voltage modulation circuit for quantum parameter amplifier's mode of operation is adjusted no longer only to be limited by pumping signal, but adjusts together through the voltage bias that voltage modulation circuit provided and pumping signal, when selecting suitable bias voltage and pumping signal, can make each kind of irrelevant signal that produces in the quantum parameter amplifier all can with treat that the amplified signal keeps the distance that can be by the wave filter split on the frequency spectrum, and then can eliminate these irrelevant signals, improve quantum parameter amplifier to the reading fidelity of qubit reading signal.
Drawings
Fig. 1 is a schematic structural diagram of a quantum parametric amplifier provided by an embodiment of the present invention;
fig. 2 is a schematic circuit diagram of a quantum parametric amplifier according to an embodiment of the present invention;
fig. 3 is a schematic circuit diagram of a quantum parametric amplifier according to another embodiment of the present invention.
Detailed Description
The embodiments described below by referring to the drawings are exemplary only for explaining the present invention, and should not be construed as limiting the present invention.
Referring to fig. 1, an embodiment of the present invention provides a quantum parametric amplifier, which includes a first capacitance module 100, a transmissive microwave cavity 200, a second capacitance module 300, and a superconducting quantum interference device 400 of an adjustable inductor, which are used to form an oscillation amplification circuit; the first capacitor module 100, the transmission-type microwave resonant cavity 200 and the second capacitor module 300 are sequentially connected, one end of the superconducting quantum interference device 400 of the adjustable inductor is connected to the middle of the transmission-type microwave resonant cavity 200, and the other end is grounded; and the resonance frequency of the transmissive microwave resonator 200 can be made equal to the frequency of the signal to be amplified by adjusting the inductance of the superconducting quantum interference device 400 of the adjustable inductance, wherein: the signal to be amplified is coupled from the first capacitor module 100 into the oscillation amplifying circuit, and the oscillation amplifying circuit amplifies the signal to be amplified under the action of the pumping signal and generates a plurality of idle frequency signals; the quantum parametric amplifier further comprises a voltage modulation circuit 500; the voltage modulation circuit 500 is arranged at one end of the superconducting quantum interference device 500 of the adjustable inductor, which is close to the transmission type microwave resonant cavity 200; the superconducting quantum interferometer device 400 with adjustable inductance can release at least one idler generated in the oscillation amplifying circuit under the action of the bias voltage provided by the voltage modulation circuit 500.
Compared with the prior art, the utility model provides a quantum parametric amplifier, including the first electric capacity module 100, transmission-type microwave resonant cavity 200, second electric capacity module 300, the superconductive quantum interference device 400 and the voltage modulation circuit 500 of adjustable inductance that are used for making up the oscillation amplification circuit; the first capacitor module 100, the transmission-type microwave resonant cavity 200, and the second capacitor module 300 are sequentially connected, one end of the superconducting quantum interference device 400 of the adjustable inductor is connected to the middle of the transmission-type microwave resonant cavity 200, and the other end is grounded, and the voltage modulation circuit 500 is disposed at one end of the superconducting quantum interference device 400 of the adjustable inductor, which is close to the transmission-type microwave resonant cavity 200; the inductance of the superconducting quantum interference device 400 with adjustable inductance is adjusted to make the resonant frequency of the transmission-type microwave resonant cavity 200 equal to the frequency of the signal to be amplified, so that the signal to be amplified and the pumping signal perform nonlinear interaction in the transmission-type microwave resonant cavity 200 to further amplify the signal to be amplified, and after the signal to be amplified and the pumping signal perform nonlinear interaction, the output signal not only includes the signal to be amplified, but also includes various idle frequency signals fiThe frequency f of the pump signal for bringing the quantum parametric amplifier into an optimum operating mode when a bias voltage is appliedpNeed not be selected as the signal f to be amplifiedsSo that when the pump signal frequency is selected and amplifiedEach idler f output when the signal frequency has a distance which can be split by a filteriAre also all related to the signal f to be amplifiedsHave the distance that can be by the wave filter split, the utility model discloses a set up voltage modulation circuit 500 for quantum parameter amplifier's operating mode is adjusted no longer only to be limited by the pumping signal, but adjusts together through the voltage bias that voltage modulation circuit provided and pumping signal, when selecting suitable bias voltage and pumping signal, can be so that each kind of irrelevant signal that produces in the quantum parameter amplifier all can with treat that the amplified signal keeps the distance that can be by the wave filter split on the frequency spectrum, and then can eliminate these irrelevant signals, improve quantum parameter amplifier to the reading fidelity of qubit reading signal.
It should be noted that, in the field of quantum computing, in order to obtain an operation result of a quantum chip, a signal output by the quantum chip, i.e., a qubit read signal, needs to be collected and analyzed, taking a superconducting qubit system as an example, a qubit read detection signal is usually in a frequency band of 4-8GHz, and has a power as low as-140 dBm or less, and even reaches-150 dBm or less. Considering the coupling efficiency of the qubit detection signal to the qubit reading detector, a power of-150 dBm to-140 dBm corresponds to a photon count inside the detector of about 1-10. Such weak detection signals are additionally lost after being transmitted again through the detector. Therefore, one of the core problems to be solved in the application of quantum chips is how to extract effective quantum state information from such weak qubit reading signals.
It is assumed that the qubit read signal that eventually leaves the qubit read detector has 10 valid photons that will enter the subsequent lines, mixing with thermal noise, electrical noise, etc. Where the standard thermal noise satisfies the thermodynamic distribution, it can be used
Converted into a photon number n, k in the above formulaBBoltzmann constant, T ambient noise temperature at frequency f, h planckian constant. Suppose the quantum chip is at a temperature of 10mKEnvironment, n is less than 0.1 and can be ignored according to the above formula, however, the receiving system of the qubit reading signal is at room temperature, n is about 1000, and if the qubit reading signal is directly transmitted out, the qubit reading signal can be submerged in noise. Therefore, the use of a parametric amplifier is necessary.
Any amplifier will additionally introduce noise while amplifying the original signal. We usually measure the equivalent temperature of the noise, i.e. the noise, and the larger the index, the worse the noise. The amplifier must deteriorate the signal-to-noise ratio and therefore the amplifier should be set to raise the gain of the amplifier as much as possible while controlling the noise temperature of the amplifier.
Noise temperature is also satisfied
Thus, we can translate the noise temperature into the number of noise photons at frequency f. Whereas the signal-to-noise ratio can be described as the ratio of the number of signal photons to the number of noise photons.
The amplifier which is commercially available at present has the best performance, and is a low noise amplifier produced by the Swedish LNF company, and can amplify signals in a 4-8GHz frequency band, and the noise temperature is about 3K. In this measure, the number of noise photons is about 10, so the maximum achievable signal-to-noise ratio using commercial amplifiers is about 1, and the best quantum parametric amplifiers can achieve the noise level of the standard quantum limit, i.e., n is 0.5. Generally, n fluctuates within 0.5-2. Therefore, the signal-to-noise ratio of the system can be improved by about 5-20 times by using the quantum parameter amplifier.
Although the quantum parameter amplifier solves the problem of extracting effective quantum state information from such a weak qubit reading signal by greatly improving the signal-to-noise ratio, a new problem is brought. The existing quantum parametric amplifier works based on a nonlinear frequency mixing principle, and in order to effectively amplify a qubit read signal, a pumping signal with a frequency close to the frequency of a signal to be amplified or a frequency doubling of the signal needs to be additionally applied when the quantum parametric amplifier works in an optimal mode, for example, a four-wave frequency mixing working mode corresponds to the applied pumping signal close to the signal to be amplified, and a three-wave frequency mixing working mode corresponds to the applied pumping signal close to twice the frequency of the signal to be amplified.
In the working process of the prior quantum parametric amplifier, a signal f to be amplified is inputsAnd a pump signal fpSignal f to be amplifiedsAt the pump signal fpAmplifying under the action of the first harmonic oscillator, outputting a signal to be amplified, and simultaneously, based on the nonlinear frequency mixing principle, outputting signals also comprising various idle frequency signals fiSignal f to be amplifiedsPump signal fpAnd an idler fiWill satisfy the formula: mf (m) ofs+nfi＝lfpWherein: m, n and l are integers, and when m, n and l take different values, different idlers f are obtainedi. At the same time, the signal f to be amplifiedsOr the pump signal fpSignals are generated in the quantum parametric amplifier based on the nonlinear principle, and are included in the output signal, which may also affect the accurate acquisition of the signal to be amplified in the output signal. When the existing quantum parametric amplifier works, the pumping signal frequency must be selected to be the frequency multiplication of the amplified signal frequency to obtain the best amplification effect, for example, when the quantum parametric amplifier is in the four-wave mixing mode, i.e. the pumping signal fpFrequency selection close to the signal f to be amplifiedsFrequency of (1), f in the idlerp、2fp-fs、2fs-fpBecause of the proximity of the signal f to be amplifiedsAffecting the acquisition of the signal to be amplified; when the quantum parametric amplifier is in the three-wave mixing mode of operation, i.e. the pump signal fpFrequency selection is close to 2 times of signal f to be amplifieds1/2f in the idlerp、fp-fsBecause of the proximity of the signal f to be amplifiedsAffecting the acquisition of the signal to be amplified.
Specifically, referring to fig. 1 and fig. 2, a quantum parametric amplifier according to an embodiment of the present invention is provided, where the quantum parametric amplifier includes a first capacitor module 100, a transmissive microwave cavity 200, a second capacitor module 300, and a superconducting quantum interference device 400 of an adjustable inductor, which are connected in sequence, where the first capacitor module, the transmissive microwave cavity 200, the second capacitor module, and the superconducting quantum interference device 400 of the adjustable inductor are connected in series, and one end of the superconducting quantum interference device 400 of the adjustable inductor is connected to the middle of the transmissive microwave cavity 200, and the other end of the superconducting quantum interference device is grounded; and the inductance of the superconducting quantum interference device 400 of the adjustable inductance can be adjusted to make the frequency of the transmission type microwave resonant cavity 200 equal to the frequency of the signal to be amplified, wherein: the signal to be amplified is coupled from the first capacitor module 100 into the oscillation amplifying circuit, and the oscillation amplifying circuit amplifies the signal to be amplified under the action of the pumping signal and generates a plurality of idler signals.
It should be noted that each of the idlers satisfies the following formula:
mfs+nfi＝lfp
wherein: m, n, l are integers, fsFor the frequency, f, of the signal to be amplifiedpFor the frequency, f, of the pumping signaliFor the frequency of the idler, it should be noted that the above formula is based on the nonlinear mixing principle when the signal f to be amplifiedsAnd a pump signal fpWhen determined, m, n and l take different values, and various idlers f are obtainedi。
Wherein, first electric capacity module 100 is arranged in will treating that the signal coupling of enlargiing gets into in transmission-type microwave resonant cavity 200, second electric capacity module 300 is used for the output signal, it needs to explain that, microwave resonant cavity must be connected with outer circuit and constitutes the microwave system just can work usually, must establish the oscillation in the chamber by the microwave signal excitation in the outer circuit, and the oscillation in the chamber must just can export to external load through the coupling again, adopt electric capacity module and microwave resonant cavity to establish the coupling usually, in this embodiment first electric capacity module 100 with second electric capacity module 300 can select for use interdigital electric capacity, distributed electric capacity or parallel electric capacity respectively, the utility model discloses to the concrete form of first electric capacity module 100 with second electric capacity module 300 does not do the restriction.
It should be noted that the oscillation amplification circuit is a common structure in the field of signal amplification and is a key component of many electronic devices, and the oscillation amplification circuit is usually represented as an LC oscillation circuit, including interconnected capacitors and inductors, which can be used for generating signals of specific frequencies as well as separating signals of specific frequencies from more complex signals. In the field of quantum computing, in order to obtain an operation result of a quantum chip, a signal output by the quantum chip, namely a qubit read signal, needs to be collected and analyzed, the qubit read signal is usually very weak and needs to be amplified, because the qubit read signal belongs to a high-frequency signal and has a very short wavelength, and because a lumped LC oscillating circuit uses a capacitive-inductive device with a large structural size and the energy of the LC oscillating circuit is dispersedly distributed in a surrounding space, the dissipation speed is very high, we must use a quantum parametric amplifier used in the quantum field.
Generally, a quantum parametric amplifier includes a capacitor, a microwave resonant cavity, a superconducting quantum interferometer and a magnetic flux bias adjusting circuit for modulating the superconducting quantum interferometer, which are connected in sequence, wherein one end of the superconducting quantum interferometer far away from the resonant cavity is grounded, and the basic principle is as follows: the alternating current generated in the superconducting quantum interferometer is utilized to form an inductor which forms an LC oscillation circuit with a capacitor, so that a single-mode optical field is constructed in the microwave resonant cavity, a weak signal to be amplified and a pumping signal enter a device together, the signal to be amplified in the microwave resonant cavity is amplified, and meanwhile, the whole process is in a superconducting state and almost has no dissipation.
Wherein: it should be noted that the superconducting quantum interferometer is a closed-loop device formed by connecting several josephson junctions in parallel, wherein: josephson junctions are generally formed by sandwiching two superconductors with a thin barrier layer, such as the S (superconductor) -I (semiconductor or insulator) -S (superconductor) structure, abbreviated as SIS, in which superconducting electrons can tunnel through the semiconductor or insulator from one side of one of the superconductors to the superconductor on the other side, or the josephson effect, and the resulting current is called josephson current, which forms a josephson interferometer, or superconducting quantum interferometer, when several josephson junctions are connected together to form a closed loop device.
The quantum parametric amplifier further comprises a voltage modulation circuit 500; the voltage modulation circuit 500 is arranged at one end of the superconducting quantum interference device 400 of the adjustable inductor, which is close to the transmission-type microwave resonant cavity 200; the superconducting quantum interferometer device 400 with adjustable inductance can release one of the idlers generated in the oscillation amplifying circuit under the action of the bias voltage provided by the voltage modulation circuit 500.
It should be noted that, when a voltage bias is applied to two ends of the superconducting quantum interferometer, the current passing through the josephson junction is an alternating oscillating superconducting current, and the oscillation frequency (or josephson frequency) will be proportional to the bias voltage, which makes the josephson junction have the ability to radiate or absorb electromagnetic waves, and it satisfies the following relation:
2eV＝hf
wherein: h is the Planck constant.
Since the superconducting quantum interferometer device composed of several josephson junctions connected in parallel has the ability to absorb electromagnetic waves, when a voltage bias is applied to the superconducting quantum interferometer device 400 with adjustable inductance, the pair of current couperots on the josephson junctions tunnels energy absorbing microwave signals out through the josephson junctions to the ground, when the voltage bias is properly selected, so that f in the relation 2eV ═ hf is equal to the frequency of one of the idlers generated by the oscillation amplifying circuit, and the idler generated in the oscillation amplifying circuit is completely absorbed and appears as the idler is released.
It should be noted that, the working process of the present invention is as follows, by adjusting the inductance of the superconducting quantum interferometer 400 with adjustable inductance, the working resonant frequency of the transmission-type microwave cavity 200 is made to be consistent with the frequency of the signal to be amplified, so that the resonant amplification effect of the signal to be amplified in the transmission-type microwave cavity 200 is the best, the signal to be amplified and the pump signal are coupled into the transmission-type microwave cavity 200, the signal to be amplified will be amplified under the action of the pump signal, it should be noted that the output signal includes not only the amplification signal, but also the pump signal, the half-frequency pump signal, the frequency-doubled pump signal and various idler signals, when applying a suitable voltage bias, the relation 2 eV-hf will be satisfied, where f is equal to the frequency of one of the idlers, the idler signal generated in the oscillation amplification circuit will be completely absorbed, as if the idler were released.
It should be noted that the utility model discloses quantum parameter amplifier need design various parameters before work, including the frequency of selecting voltage offset size and pumping signal, one of the final objectives of the utility model is that make all can not treat among the irrelevant signal of output and enlarge the signal and cause the interference, also even they can be split by the wave filter, provide a specific example here, when treating to enlarge the signal frequency and be 4GHz, at first can design one of them idle frequency signal and be 2GHz, calculate through relation 2eV ═ hf and obtain voltage offset, again according to formula mfs+nfi＝lfpCalculating to obtain one possible pump signal frequency, for example, when m, n, and l are all 1, selecting the pump signal frequency to be 6GHz, and then according to the formula mfs+nfi＝lfpConsidering other possible idlers, it can be shown that when m, n and l take different values, the resulting idler fiWill not treat the amplified signal fsCausing interference. The following table shows the signals f to be amplified generated when the frequency of the signal to be amplified is 4GHz and the frequency of the pump signal is 6GHzs8 idlers f with the closest frequencyi。
Table 1: 8 kinds of idle frequency signals fi
From the above table, the signal f to be amplified is generateds8 idlers f with the closest frequencyiAre all in accordance with the signal f to be amplifiedsKept at a distance, then other idlers f are generatediWill not treat the amplified signal fsCausing interference.
The traditional quantum parametric amplifier has another problem that when an actual quantum chip works, a large number of quantum bit signals need to be read out simultaneously, quantum state information of each quantum bit is carried and transmitted by an independent signal, and the frequency of the quantum state information carrying signal is different from the frequency of quantum state information carrying signals of other quantum bits. Reading multiple qubits simultaneously means that multiple signals to be amplified carrying information need to pass through a quantum parameter amplifier. Each of which produces a plurality of extraneous signals while obtaining an amplification effect, and at least one of which is close to the signal to be amplified. In addition, an extraneous signal generated from a signal to be amplified is likely to be additionally close to the frequency of another signal to be amplified.
Specifically, for example: input of a signal f to be amplified of a conventional quantum parametric amplifiersRespectively having a frequency of 6.4GHz and 6.58GHz (0.18 GHz apart, filter separable), a conventional quantum parametric amplifier pump signal fpCan be designed to be 6.5GHz corresponding to a four-wave mixing mode of operation, then according to the formula mfs+nfi＝lfpAmplified signal f of 6.4GHzsOne of the idlers fiAt 6.6GHz, the 6.58GHz signal will be affected (at 0.02GHz distance, it is difficult to split).
When the quantum parametric amplifier of the present invention is adopted, an idle frequency signal, such as 4GHz, is designed according to the 4GHz signal and the 6.4GHz amplified signal fsDesigning the pump signal fpAt 5.2GHz and a bias voltage, it can be seen that the 5.2GHz pump signal fpAmplified signal f corresponding to 6.4GHz and 6.58GHz respectivelysMixing the signals to obtain all idlers fiAmplified signal f equal to both 6.4GHz and 6.58GHzsKeeping a detachable distance.
Further, the superconducting quantum interference device 400 of the adjustable inductor comprises a superconducting quantum interferometer 410 and a magnetic flux modulation circuit 420 which are connected in a mutual inductance coupling manner, and particularly, refer to fig. 2; the superconducting quantum interferometer 410 is a closed-loop device formed by connecting a plurality of Josephson junctions in parallel; the flux modulation circuit 420 is used to adjust the inductance of the superconducting quantum interferometer 410 by adjusting the magnetic flux of the closed loop device.
The magnetic flux modulation circuit 420 comprises a magnetic flux modulation line and a current device for generating a bias current which are connected in sequence; wherein: the flux modulation lines are used to carry the bias current and to mutually inductively couple the bias current to the superconducting quantum interferometer 410.
It should be noted that, the current device for generating the bias current may be a current source, or a voltage source and a resistor which are connected in sequence and can provide the bias current, and the present invention is not limited to the specific form of the current source.
Further, the transmission-type microwave resonant cavity 200 is a coplanar waveguide microwave resonant cavity with a length of one half of the wavelength of the signal to be amplified, and a coplanar waveguide microwave resonant cavity with a length of one half of the wavelength of the signal to be amplified is adopted, because the highest electric field intensity of the half-wavelength coplanar waveguide microwave resonant cavity is respectively located at one end close to the first capacitor module 100 and one end close to the second capacitor module 300, and the electric field at the middle position is almost 0, a direct current voltage bias is introduced at the electric field intensity position so as not to influence the microwave in the transmission-type microwave resonant cavity 200, an output signal is output from one end close to the second capacitor module 300, and the signal to be amplified by adopting the quarter-wavelength reflection-type resonant cavity is amplified at the strongest position, and a half-wavelength coplanar waveguide microwave resonant cavity is adopted, and the signal to be amplified is amplified at the position where the signal is absorbed weakest in the transmission-type resonant cavity 200, thereby improving the signal amplification gain.
Preferably, as shown in fig. 2, the transmissive microwave cavity 200 may be formed by a pair of coplanar waveguide microwave cavities 210 having a length of one quarter of the wavelength of the signal to be amplified, which are connected in series.
In the microwave field, the coplanar waveguide is three parallel metal thin film conducting strip layers prepared on the surface of a dielectric layer, wherein the conducting strip layer positioned in the center is used for transmitting microwave signals, the conducting strip layers on two sides are connected to a ground plane, the biggest difference with the general circuit is that the coplanar waveguide is a distributed circuit element, the capacitance/inductance/reactance/impedance of the distributed circuit element is uniformly distributed along the signal propagation direction of the coplanar waveguide, the coplanar waveguide propagates TEM waves, and the impedance of the waveguide is equal everywhere along the signal propagation direction, so that no signal reflection exists, and signals can almost pass without loss; in addition, coplanar waveguides have no cutoff frequency, while common lumped circuits have cutoff frequencies. For a section of uniform coplanar waveguide, most microwave signals in the frequency range can be transmitted smoothly, and the section of uniform coplanar waveguide is called a transmission line, namely a coplanar waveguide transmission line. When the designed coplanar waveguide transmission line has a certain length, and a capacitance node is respectively constructed at two ends of the coplanar waveguide transmission line, the microwave signal is reflected after encountering the node, resonance is formed in the section of transmission line, and a resonant cavity is formed.
Preferably, the flux modulation line for transmitting the bias current may also use a coplanar waveguide transmission line.
Further, referring to fig. 3, in order to filter out extraneous signals other than the amplified signal in the output signal, a filter 600 is further disposed at the signal output terminal of the second capacitor module 300, wherein the extraneous signals mainly refer to a pump signal, a half-frequency pump signal, a frequency-doubled pump signal, and various idlers.
It should be noted that, the conventional quantum parametric amplifier can achieve the maximum amplification effect only when the frequency of the pump signal is equal to an integral multiple of the frequency of the signal to be amplified. And under the corresponding three-wave mixing working mode, the frequency of the pumping signal is equal to the frequency of the signal to be amplified. In the four-wave mixing mode of operation, the frequency of the pump signal is equal to twice the frequency of the signal to be amplified. In the three-wave mixing mode, the pump signal and the amplified signal in the output signal are not well distinguished. In the four-wave mixing mode, the half-frequency pump signal and the amplified signal in the output signal are not well distinguished. Adopt the utility model relates to a quantum parameter amplifier, quantum parameter amplifier's mode of operation is adjusted no longer only to be restricted to the pumping signal, but adjust together through voltage modulation circuit and pumping signal, when selecting suitable bias voltage and pumping signal, can be so that each kind of irrelevant signal that produces in the quantum parameter amplifier all can with treat that the amplified signal keeps the distance that can be by the wave filter split on the frequency spectrum, and then can adopt these irrelevant signals of convenient elimination of back level wave filter, improve quantum parameter amplifier to quantum bit read signal's reading fidelity.
The structure, features and effects of the present invention have been described in detail above according to the embodiment shown in the drawings, and the above description is only the preferred embodiment of the present invention, but the present invention is not limited to the implementation scope shown in the drawings, and all changes made according to the idea of the present invention or equivalent embodiments modified to the same changes should be considered within the protection scope of the present invention when not exceeding the spirit covered by the description and drawings.
Claims (11)
1. A quantum parametric amplifier is characterized in that the quantum parametric amplifier comprises a first capacitor module, a transmission type microwave resonant cavity, a second capacitor module and a superconducting quantum interference device with adjustable inductance, wherein the first capacitor module, the transmission type microwave resonant cavity, the second capacitor module and the superconducting quantum interference device are used for forming an oscillation amplification circuit; the first capacitor module, the transmission-type microwave resonant cavity and the second capacitor module are sequentially connected, one end of the superconducting quantum interference device of the adjustable inductor is connected to the middle of the transmission-type microwave resonant cavity, and the other end of the superconducting quantum interference device of the adjustable inductor is grounded; and the resonance frequency of the transmission type microwave resonant cavity can be equal to the frequency of a signal to be amplified by adjusting the inductance of the superconducting quantum interference device with the adjustable inductance, wherein: the signal to be amplified is coupled into the oscillation amplifying circuit from the first capacitor module;
the quantum parametric amplifier also comprises a voltage modulation circuit;
the voltage modulation circuit is arranged at one end, close to the transmission type microwave resonant cavity, of the superconducting quantum interference device of the adjustable inductor;
the superconducting quantum interferometer device with the adjustable inductance can release at least one idler signal generated in the oscillation amplifying circuit under the action of the bias voltage provided by the voltage modulation circuit.
2. The quantum parametric amplifier of claim 1, wherein the tunable-inductor superconducting quantum interference device comprises a mutual inductance coupling connected superconducting quantum interferometer and a flux modulation circuit;
the superconducting quantum interferometer is a closed-loop device formed by connecting a plurality of Josephson junctions in parallel;
the magnetic flux modulation circuit is used for adjusting the magnetic flux of the closed loop device so as to adjust the inductance of the superconducting quantum interferometer.
3. A quantum parametric amplifier according to claim 2, wherein the superconducting quantum interferometer is a closed loop device consisting of two josephson junctions connected in parallel.
4. A quantum parametric amplifier according to claim 2, wherein the flux modulating circuit comprises a flux modulating line and a current device for generating a bias current connected in series;
wherein: the flux modulation lines are used for transmitting the bias current and enabling the bias current to be mutually inductively coupled with the superconducting quantum interferometer.
5. A quantum parametric amplifier according to claim 4, wherein the flux modulation line is a coplanar waveguide microstrip transmission line.
6. A quantum parametric amplifier according to claim 4, wherein the current device is a current source or a voltage source and a resistor connected in series to provide the bias current.
7. A quantum parametric amplifier according to claim 2, wherein a pump signal for amplifying the signal to be amplified is coupled from the first capacitance module or the flux modulation circuit into the oscillation amplification circuit.
8. A quantum parametric amplifier according to claim 1, wherein the first and second capacitance modules are each one of interdigital, distributed, and parallel capacitors.
9. A quantum parametric amplifier according to claim 1, wherein the transmissive microwave cavity is a coplanar waveguide microwave cavity with a length of one-half the wavelength of the signal to be amplified.
10. A quantum parametric amplifier according to claim 1, wherein the transmissive microwave cavity is formed by a pair of coplanar waveguide microwave cavities in series, each of which has a length of one quarter of the wavelength of the signal to be amplified.
11. A quantum parametric amplifier according to any of claims 1-10, further comprising a filter;
the filter is arranged at one end, far away from the transmission type microwave resonant cavity, of the second capacitor module.
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| CN110120792A (en) * | 2019-06-17 | 2019-08-13 | 合肥本源量子计算科技有限责任公司 | A kind of quantum parameters amplifier |
| CN110277969A (en) * | 2019-06-17 | 2019-09-24 | 合肥本源量子计算科技有限责任公司 | A kind of quantum parameters amplifier |
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Cited By (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN110120792A (en) * | 2019-06-17 | 2019-08-13 | 合肥本源量子计算科技有限责任公司 | A kind of quantum parameters amplifier |
| CN110277969A (en) * | 2019-06-17 | 2019-09-24 | 合肥本源量子计算科技有限责任公司 | A kind of quantum parameters amplifier |
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