CN116187461A - Bit structure, quantum chip, manufacturing method of quantum chip and quantum computer - Google Patents
Bit structure, quantum chip, manufacturing method of quantum chip and quantum computer Download PDFInfo
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Abstract
The application discloses a bit structure, a quantum chip, a manufacturing method of the bit structure and the quantum chip and a quantum computer, and belongs to the field of quantum computing. The bit structure includes a qubit and a frequency regulation circuit coupled thereto. Wherein the frequency modulation circuit is coupled to the qubit without additional connection and is constructed based on a superconducting quantum interferometer. The bit structure can realize controllable adjustment of the quantum bit frequency, and can avoid adverse effect of noise introduced during adjustment and control on the coherence time.
Description
Technical Field
The application belongs to the field of quantum information, in particular to the technical field of quantum computing, and particularly relates to a bit structure, a quantum chip, a manufacturing method thereof and a quantum computer.
Background
The quantum bit on the quantum chip is a basic unit for executing quantum computation, and the quantum bit performance can be adjusted by regulating and controlling the frequency of the quantum bit, so that a series of operations are realized. In general, superconducting qubits have capacitance and superconducting quantum interferometers, and the maximum frequency of the qubit can be regulated by capacitance charging energy and josephson energy. Accordingly, in order to control the frequency of the qubit, a dc bias line needs to be configured. But the flux noise generated by the dc bias line can adversely interfere with the phase decoherence time of the qubit.
Disclosure of Invention
Examples of the present application provide a bit structure, a quantum chip, a method of fabricating the same, and a quantum computer. The method can adjust the frequency of the qubit and simultaneously weaken and even avoid adverse interference of the frequency adjustment existing in the qubit on the decoherence time of the qubit phase.
The solution illustrated in the present application is implemented in the following manner.
In a first aspect, the present examples provide a bit structure. It comprises the following steps:
a qubit without a frequency adjustment structure, the qubit being insensitive to the magnetic flux signal such that frequency tuning of the qubit is not responsive to a direct control signal, wherein the direct control signal is directly applied to the qubit by the magnetic flux signal and is implemented as a signal operation that is frequency-dependent; and
a frequency regulation circuit configured based on the superconducting quantum interferometer, the frequency regulation circuit being coupled without additional connection to the qubit, the frequency regulation circuit configured to operate the superconducting quantum interferometer with a magnetic field to perform frequency control on the qubit.
In this bit structure, a frequency control circuit based on a superconducting quantum interferometer is used, and therefore, a magnetic flux control signal can be applied to the frequency control circuit, and the frequency of the qubit can be indirectly controlled by the frequency control circuit. Therefore, according to the scheme, magnetic flux noise existing in frequency regulation and control of the quantum bit can be avoided, and adverse effects on the coherence time of the quantum bit caused by noise can be relieved. In addition, since no additional connection is required between the frequency regulating circuit and the qubit, the process, such as configuration, connection operation, etc., of various circuits is reduced to some extent, thereby reducing the manufacturing difficulty and shortening the manufacturing period.
According to some examples of the present application, the bit structure further comprises: a read circuit coupled to the qubit and configured to perform a read operation on the qubit; and/or driving a steering circuit coupled to the qubit and configured to perform a transition excitation operation on the qubit.
According to some examples of the present application, the superconducting quantum interferometer is a radio frequency superconducting quantum interferometer or a direct current superconducting quantum interferometer.
According to some examples of the present application, the superconducting quantum interferometer is a direct current superconducting quantum interferometer and has two josephson junctions that are symmetrical.
According to some examples of the present application, the frequency modulation circuit has a capacitance, and the superconducting quantum interferometer is shunted from the capacitance.
According to some examples of the present application, a frequency regulation circuit has a frequency control element.
According to some examples of the present application, the frequency control element is a magnetic flux control wire.
According to some examples of the present application, the drive modulation circuit is a microwave control line.
According to some examples of the present application, the read circuit is a read resonator.
According to some examples of the present application, the qubit is composed of a capacitor in parallel with a single josephson junction.
According to some examples of the present application, the qubit is composed of a capacitor in parallel with a single josephson junction; and/or the frequency regulating circuit is capacitively coupled with the qubit.
According to some examples of the present application, the read circuit, the drive steering circuit, and the frequency steering circuit are each coupled to the qubit by a capacitance.
In a second aspect, the present examples provide a multi-bit device comprising at least two of the foregoing bit structures, and at least two bit structures disposed adjacent to and coupled to each other.
According to some examples of the present application, the at least two bit structures are arranged adjacent to each other and coupled to each other by an adjustable coupling structure, and the adjustable coupling structure is provided by an adjustable qubit configured with a frequency signal line.
According to some examples of the present application, all bit structures are in a one-dimensional chained arrangement and coupled in pairs in sequence; alternatively, all bit structures are in a two-dimensional network layout and there is at least one coupling unit in which one bit structure is coupled with at least two other bit structures.
In a third aspect, the present examples provide a quantum chip having the foregoing bit structure.
In a fourth aspect, the present examples provide a quantum computer comprising the quantum chip described above.
In a fifth aspect, examples of the present application provide a method of fabricating a qubit with tunable frequency and controllable tunable range. The method comprises the following steps:
selecting adjacent first and second regions on the substrate;
forming a qubit in a first area, wherein the qubit is provided by a first quantum circuit formed by connecting a first capacitor and a single Josephson junction in parallel;
manufacturing a second quantum circuit formed by connecting a second capacitor and a direct current superconducting quantum interferometer in parallel in a second area, wherein the second quantum circuit is also coupled with the first quantum circuit;
a transmission line is fabricated on the substrate that adjusts the qubit frequency, and the transmission lines are sufficiently adjacent to the dc superconducting quantum interferometers to couple to each other, thereby allowing the transmission lines to generate a magnetic field acting on the dc superconducting quantum interferometers under excitation by the drive signal.
According to some examples of the present application, a direct current superconducting quantum interferometer includes a superconducting loop and two josephson junctions in parallel, and the two josephson junctions are asymmetric.
The beneficial effects are that:
compared with the problem that the bit coherence time is shortened due to the fact that the frequency control circuit is directly configured for the quantum bit, in the example of the application, the frequency of the quantum bit is indirectly controlled through the magnetic field signal applied to the superconducting quantum interferometer by using the frequency regulation circuit based on the superconducting quantum interferometer, so that the magnetic field signal can be prevented from being directly applied to the quantum bit, and the interference of the quantum bit phase decoherence time is prevented from being adversely affected.
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For a clearer description, the drawings that are required to be used in the description will be briefly introduced below.
FIG. 1 is a schematic diagram of a structure of a qubit on a quantum chip according to the related art;
FIG. 2 is an equivalent circuit diagram of a bit structure in the examples of the present application;
FIG. 3 is a numerical simulation of a bit structure in an example of the present application;
fig. 4 is an equivalent circuit diagram of the bit structure of fig. 2 coupled by an adjustable coupler in the examples of the present application.
Reference numerals illustrate: a 100-bit structure; 101-base bits; 102-an adjustable structure; 103-read structure.
Detailed Description
Quantum chips are processors in quantum computers that perform quantum computation. The quantum chip comprises a quantum bit structure which is a processing unit of the processor. The quantum bit is a two-level system which follows the law of quantum mechanics and can be in any superposition state of 0 and 1.
Depending on the different physical systems employed to construct the qubit, the qubit includes superconducting quantum circuits, semiconductor quantum dots, ion traps, diamond vacancies, topological quanta, photons, etc. in physical implementations. Among them, superconducting quantum computation is the fastest and best solid quantum computation implementation scheme at present.
The energy level structure of the superconducting quantum circuit can be regulated and controlled by externally adding electromagnetic signals, and the design customization of the circuit is high in controllability. Meanwhile, due to the existing mature integrated circuit technology and micro-nano processing technology, the superconducting quantum circuit has scalability and advantages which are difficult to be compared with other quantum bit physical systems.
A quantum chip based on superconducting quantum circuit contains superconducting circuit structure such as quantum bit and microwave resonant cavity. The qubit is a two-level system formed by using a capacitor and a Josephson junction with nonlinear inductance characteristic. The electric parameter states of capacitance, inductance and the like of different targets are realized by designing different shapes. The shape of the Transmon qubit (transmitter qubit) is shaped like a "+" and consists of a cross-shaped capacitor and a superconducting quantum interference device (Superconducting Quantum Interference Device, short for short, required) connected to the end of one branch of the capacitor. Wherein the superconducting quantum interference device (squid) comprises one or more josephson junctions; josephson junctions are devices comprising two electrodes and a thin insulating barrier separating the two electrodes, and the materials of the two electrodes may exhibit a superconducting property at or below their own critical temperature.
In the above-described qubit architecture, there are a number of different functional circuit structures around the qubit, such as a read resonator and a coupler for coupling between the qubits.
The circuit structure further includes a drive Control signal Line (XY-Control Line, also called XY Control Line or pulse Control signal Line) for performing XY rotation operation on the qubit. By applying a driving voltage signal in the circuit, transition excitation can be performed on the qubit; which is associated with the qubit by capacitive coupling.
The circuit structure further comprises a circuit structure for performing a Z rotation operation on the qubit and is completed by a control signal line near the superconducting quantum interference device (squid); it is called a magnetic flux Control signal Line (also called a Z Control signal Line or a frequency Control signal Line). As previously mentioned, the flux modulating signal line is arranged in the vicinity of the superconducting quantum interference device (squid), which excites the current and is inductively coupled to the superconducting quantum interference device (squid) by a magnetic field.
It should be noted that both the magnetic flux controlling signal line and the drive control line may be used to control the qubit, but their control forms and purposes are essentially different.
Wherein the drive control signal line applies a pulse to the qubit in the form of an electric field, the pulse causing a transition in the energy level of the qubit.
The signal transmitted by the magnetic flux regulating signal line generates a magnetic field and is applied to the superconducting quantum interference device (squid) region, and the magnetic flux passing through the quantum interference device (squid) region can cause the critical current of squid to change. The change of the critical current causes the change of the frequency of the tunable qubit, namely, the control of the frequency of the qubit can be realized through the signal transmitted by the magnetic flux control signal line.
Fig. 1 is a schematic structural diagram of a qubit arranged on a quantum chip in the related art.
In conjunction with the structure shown in fig. 1, the qubit structure usually employs a single capacitor to ground, and a superconducting quantum interference device with one end grounded and the other end connected to the capacitor. And this capacitance is often a cross-type parallel plate capacitance.
Referring to FIG. 1, a cross-type capacitive plate C q (i.e. bit capacitance) is surrounded by a ground plane (GND) and a cross-shaped capacitive plate C q There is a gap (typically an air gap, insulation) with the ground plane (GND).
One end of the superconducting quantum interference device is connected to the cross-shaped capacitor plate C q The end of (one of the capacitive arms, as the first end mentioned later), the other end is connected to the ground plane (GND).
Due to the cross-shaped capacitive plates C q Typically for connecting to a superconducting quantum interference device, and a second end for coupling to a read resonator. Whereas cross-shaped capacitor plate C q For coupling with adjacent qubits to achieve bit expansion. A certain space is usually reserved near the first end and the second end for arranging microwave transmission lines such as a drive control signal line, a magnetic flux control signal line and the like. Likewise, a space is usually reserved in the vicinity of the resonant cavity for arranging a read signal transmission line coupled to the resonant cavity.
When quantum computation is executed, the frequency of the quantum bit is firstly adjusted to the working frequency (initial state manufacturing) by utilizing a magnetic flux adjusting signal on a magnetic flux adjusting signal line, then the quantum state adjusting signal is applied to the quantum bit in the initial state through a driving control signal line to adjust the quantum state of the quantum bit, and then the quantum state of the quantum bit after adjustment is read by adopting a resonant cavity.
Specifically, the quantum state of the qubit may be determined by applying a read probe signal (e.g., a microwave signal having a frequency of 4 GHz-8 GHz) to a read signal transmission line coupled to the resonant cavity, and then analyzing a read feedback signal (a signal responsive to the read probe signal) output via the read signal transmission line. The magnetic flux control signal line, the driving control signal line, the reading signal transmission line and other structures can adopt microwave transmission line structures, and the detailed description is omitted.
It should be noted that the quantum chip performs the quantum computation process as follows:
the waveform command and the like generated by compiling the quantum program in the quantum computing task are transmitted to the physical signal generating device. The physical signal generating means generates a corresponding physical signal and it is sent to the quantum chip to operate on the corresponding qubit. Then, a quantum state reading signal is applied to the corresponding quantum bit, quantum state information of the quantum bit is determined according to a reading feedback signal fed back by the quantum bit based on the quantum state reading signal, and finally a quantum computing result is analyzed.
As previously mentioned, the computation of qubits requires control of the qubits-e.g., frequency regulation-and is typically implemented via frequency regulation signal lines. To the best of the inventors' knowledge, a common superconducting qubit is generally composed of a capacitively shunted SQUID. Whereas SQUIDs are typically symmetric josephson junctions and thus can generate a superconducting qubit with adjustable frequency. The maximum frequency of the bit can be regulated and controlled by controlling either or both of the capacitance charging energy and the Josephson energy; by controlling the degree of asymmetry of the SQUID, the adjustable range of the bit frequency can be adjusted. However, SQUIDs with higher asymmetry require high manufacturing process requirements. For example, if the bit frequency tunable range is designed to 100MHz, then a higher asymmetric SQUID would be required to be used, but a higher asymmetric SQUID would have greater difficulty in process implementation.
Therefore, based on the special requirement of the adjustable range of the bit frequency and the consideration of reducing the difficulty of process realization, a new quantum bit structure can be selectively constructed; it is also a small range of frequency tunable bits. In general, the new qubit structure adds an adjustment control structure on the basis of a fixed bit frequency (without a Z control signal line), so that the adjustment and control of the fixed bit frequency are realized (and the adjustable range is controllable).
Further, the above scheme can achieve other advantages. For example, since the bits without the Z control signal line are designed, there is no interference of magnetic flux noise generated if the Z control signal line is used with the phase decoherence time of the bits.
Fig. 2 is an equivalent circuit diagram of a bit structure in an example of the present application. As shown in fig. 2, in the bit structure, the bit portion (referred to as the base bit 101 for convenience of description and distinction) is a capacitor (denoted as C in the figure q ) In parallel with a single josephson junction (denoted JJ in the figure) and typically in a superconducting connection.
The fundamental bit 101 therein is insensitive to the magnetic flux signal, so that the frequency change of the qubit cannot be achieved by a direct control signal. And wherein the direct control signal is directly applied to the qubit by the magnetic flux signal and is implemented as a frequency operation. In other words, if the frequency of the fundamental bit is to be adjusted, it is not possible to simply apply the magnetic flux signal directly to the fundamental bit. For example, if an attempt is made to configure a Z line for the base bit, then a dc driving signal is applied to the Z line to excite the Z line, and then the frequency of the base bit is operated by using a direct control signal generated by the excitation of the Z line. Thus, the base bits 101 may generally be described as non-tuning bits.
Meanwhile, the base bit 101 has a separate XY control line (denoted Xcontrol in the figure) and both are capacitively coupled.
Further, the base bit 101 passes through the capacitor C qt Connected/capacitively coupled to the Tunable structure 102 (e.g., labeled as Tunable in part of the figures); and the base bit 101 and the tunable structure 102 are coupled without additional connections (e.g., without sharing one or more electrodes, such as capacitive electrodes having capacitance to ground).
Wherein the tunable structure 102 is formed by a capacitor C t Split parallel SQUID (loop labeled two JJ in the figure) is constructed. The adjustable structure 102 may be considered as an adjustable bit. The base bit 101 and the adjustable circuit 102 cooperate with each other to form a tuneable bit.
And the tunable structure 102 has a separate Z control line (no separate XY control line). In order to read the bit structure 101, the read portion (read structure 103) thereof is a bit pattern formed by passing the base bit 101 through C qr Connected/capacitively coupled to the read chamber. In the example of fig. 2, the read structure 103 is constituted by a coplanar waveguide resonator in parallel with a capacitor.
Thus, in some examples, a bit structure is presented comprising: qubit and frequency regulation circuitry. Wherein the qubits have no frequency-regulating structure (i.e., no Z control line, e.g., labeled Zcontrol). The frequency control circuit is based on a superconducting quantum interferometer structure. A frequency manipulation circuit is coupled to the qubit without additional connection, the frequency manipulation circuit configured to operate the superconducting quantum interferometer with a magnetic field to implement frequency control of the qubit.
The superconducting quantum interferometer can be a radio frequency superconducting quantum interferometer, or can be a direct current superconducting quantum interferometer. The direct current superconducting quantum interferometer can directly use a magnetic flux control circuit to realize the adjustment of frequency. The radio frequency superconducting quantum interferometer can be coupled with the resonant circuit through mutual inductance; wherein the resonant tank is driven by radio frequency current through radio frequency.
For a dc superconducting quantum interferometer, which has two josephson junctions, in different examples, both may be selectively configured to be symmetrical. Alternatively, two josephson junctions may be selectively configured asymmetrically so that the frequency tuning range can be controlled.
The frequency control circuit can be further provided with a capacitor, and the superconducting quantum interferometer is shunted with the capacitor in the frequency control circuit based on the capacitor. Further, the frequency regulation circuit may also be configured with frequency control elements to direct current superconducting quantum interferometers (DC-SQUIDs). In which the frequency control element is, for example, magneticAnd (5) connecting a control line. To achieve the correlation/signal cooperation of the adjustable structure and the underlying bits with each other, the adjustable structure may use a capacitance C, for example qt Capacitive coupling is achieved with the base bit.
To enable reading of the result after quantum computation is performed on the new bit structure, it may further be taken to configure a read structure/read circuit in the bit structure to perform a read operation on the quantum bit. The read circuit is, for example, a read resonator. Further, a capacitor connected in parallel with the read resonator may also be configured in the read circuit. On the basis, the reading circuit and the basic bit pass through the capacitor C qr Capacitive coupling is achieved.
Similarly, to operate on a qubit such as Z-rotation, it may be assumed that drive steering circuitry is configured in the bit structure so as to be configured to perform transition-excited operations on the qubit. For example, the drive modulation circuit is a microwave control line (XY control line, e.g., labeled xcontrol) that may be capacitively coupled to the base bit through a capacitor.
In the bit structure, the various lines, components, and the like therein may be various suitably selected transmission lines, such as coplanar waveguide line transmission lines. In the system of superconducting quantum computers, the materials of these wires and components may be formed of superconductor materials exhibiting superconducting properties, such as aluminum, niobium, tantalum, or titanium nitride, etc., at temperatures equal to or below the critical temperature, such as at about 10-100 millikelvin (mK) or about 4K; the superconductor materials are not limited to the above listed ones, and materials exhibiting superconducting properties at a temperature equal to or lower than the critical temperature may be used as desired.
The josephson junctions are, for example, tunnel junctions, point contacts and various microbridge junctions. The various lines and components may alternatively be fabricated on one or more surfaces of a single layer substrate, a double layer substrate, or a multi-layer substrate (substrate or described as substrate/base), or even partially or fully below the surface of the substrate. As a specific and alternative example, the material of the substrate is, for example, sapphire or a high-resistance silicon material.
In the structure shown in fig. 2, the bit structure 100 is additionally provided with a control structure/tunable structure 102 in comparison to a general qubit for the bit structure 100; and the tunable structure is coupled to the base bit 101 by capacitive coupling. Wherein the coupling of the control structure to the base bit may be configured as a dispersive coupling so as to avoid direct exchange of energy between the two. In order to achieve dispersive coupling, the frequency of the fundamental bit and the frequency of the tunable structure may be selected to be far more mismatched (the frequency of the fundamental bit is greater than the frequency of the tunable structure) than the coupling strength between the two, i.e., to satisfy the following equation 1:
Δ＞＞g
wherein delta is the amount of mismatch between the base bit and the tunable structure and g is the coupling strength between the base bit and the tunable structure.
The frequency of the bit structure 100 is the bit frequency omega at the base bit 101 q The frequency exhibited after being affected by the tunable structure 102. The tunable structure 102 as described above may be functionally described as a qubit, and thus has a bit frequency ω t And no separate XY control line is set, defaulting to always be at |0>A state. Considering the dispersive coupling of the fixed frequency bit/fundamental bit to the tunable structure, the resonant frequency of the fixed bit frequency can be modified as follows:
ω′ q ＝ω q -χ
Δ＝ω q -ω t
since the base bit 101 of the bit structure 100 has only a single XY control line and the base bit has no single Z control line, the functional analogue of the Z control line is configured to the tunable structure. Therefore, the direct interference of magnetic flux noise of the Z control line to the frequency of the basic bit can be avoided, and the phase withdrawal of the bit is greatly promotedCoherence time
This is because the adjustable range of the frequency of the bit structure 100 is determined by the frequency of the adjustable structure. The frequency of the tunable structure is determined by the Z control line, so that the magnetic flux noise of the Z control line has less modification/influence on the frequency of the bit structure 100. And this degree of influence is much smaller than the direct influence of the bit frequency of the Z control line being directly configured independently. It is therefore believed that the introduction of the adjustable structure can greatly reduce the effect of the magnetic flux noise of the Z control line on the bit phase decoherence time. In addition, the weak adjustability of the bit frequency can be achieved by controlling the dispersive coupling strength of the bit to the tunable structure and the frequency of the tunable structure.
To verify the above structure, numerical simulation is now performed:
the bit capacitance and the shunt capacitance of the frequency regulation circuit are 88fF, and the coupling capacitance between the base bit and the adjustable structure is 10fF. The critical current of the josephson junction of the fundamental bit is about 38nA; the critical current of the josephson junction of the tunable structure SQUID is about 15nA.
By numerical simulation (as shown in fig. 3), bit structure 100 is tunable between approximately 5.38GHz to 5.51GHz, and the tunable amplitude is 134MHz. The amplitude may be further adjusted by further adjusting the parameter such that the adjustable amplitude is larger. Meanwhile, most areas in the whole adjusting period can be seen to meet the dispersion coupling condition, and when the magnetic flux bias is 0, the adjustable structure frequency is the largest, the detuning amount is the smallest, and the dispersion condition is weaker.
As can be appreciated based on the above description, the bit structure can achieve a slightly adjustable frequency of bits based on the state of the art of existing micro-nano processing techniques, and the adjustable amplitude (adjustable range) is also controllable; i.e. by operating the adjustable structure, it is possible to obtain qubits with different adjustable ranges that can be adjusted. That is, to the knowledge of the inventors of the present application, the existing qubit with the frequency adjustable range is fixed once it is fabricated, and cannot be adjusted as required during the use of the qubit; however, by the scheme of the application, after the bits are manufactured, the bits can be controlled as required to obtain different frequency adjustable ranges.
In particular, since the base bit itself does not have an independent Z control line, and on the other hand the Z control line is configured on the adjustable structure, the phase decoherence time of the bit structure can be kept at a good level.
For the reading process of the bit structure, reference may be made to the reading of superconducting qubits of the conventional transmon (transmitter) type. Considering that the adjustable range of the frequency of the bit structure is relatively small, a more accurate measurement can be considered in testing the modulation spectrum of the bit structure.
In addition, in order to realize larger quantum integration, a plurality of bit structures can be selected to be coupled and integrated; for example, at least two bit structures are disposed in close proximity and coupled to each other. In some examples, an adjustable coupler may be used to implement the coupling connection of two bit structures, see fig. 4; in other examples, the coupler may also be a non-tunable coupler. The tunable coupler may be provided by a tunable qubit configured with a frequency signal line.
In fig. 4, coupler represents an adjustable Coupler; it is used for adjusting the coupling strength between a first bit structure (Qubit 1) and a second bit structure (Qubit 2) so that the coupling strength between the two bits reaches an on (a set coupling strength can be reached) and off state. Qubit1 and Qubit2 are connected to each other by a capacitor (C 37 ) Coupled and also respectively through a capacitor (C 34 、C 47 ) Coupled to the adjustable coupler.
In fig. 4, the two josephson junctions of the superconducting quantum interferometer in the copuller are configured as symmetrical junctions; but as an advantageous attempt preferably the two josephson junctions described above are configured as asymmetric junctions; a weakly tunable structure can be realized based on asymmetric junctions. Thus, the direct current superconducting quantum interferometer comprises a superconducting loop and two Josephson junctions connected in parallel, and the two Josephson junctions are asymmetric; it is often shown that the two josephson junctions differ in area and that the critical currents in the circuit are different for both.
In other words, in the configuration of fig. 4, the adjustable coupler is identical to the adjustable configuration of fig. 2 (in other examples, it may be adjusted to couplers of other configurations as well). But the adjustable coupler may also be replaced by a weak adjustable structure. And, correspondingly, the coupling capacitance between the reasonable bits and the Coupler (taking into account the reduction of the frequency difference between the tunable coupling on and off points) is set and the on and off points are placed at two flux insensitive points of the weakly tunable structural frequency, respectively.
In the open coupling position, the frequency of the coupler has a very large effect on the effective coupling strength between two bits. A slight change in the frequency of the coupler at this location may result in a large change in the effective coupling strength between the two bits. And the two-bit gate requires a relatively stable effective coupling strength, it is necessary to set the frequency of the coupler at the point of magnetic flux insensitivity when the coupler is turned on to perform two-bit coupling. Therefore, the difficulty of measuring the effective coupling strength (the coupling open position can not be found in the actual use process of the traditional adjustable coupler) of a tester in the test can be reduced, and the stable coupling open frequency position can be provided for the two-bit gate operation.
When more bit structures are configured, the bit structures may take a one-dimensional chained arrangement or a two-dimensional network arrangement. In the example of a one-dimensional chain layout, it may be that all bit structures are associated with each other in a coupled manner in sequence every two-by-every-one-dimensional chain may be formed. Alternatively, in the structure of the one-dimensional chain layout, part of the bit structures are coupled to each other, and the other bits may be uncoupled from each other. Similarly, in a two-dimensional network layout scheme, all bit structures may be associated with each other, i.e., coupled, or some may be coupled while the remaining bit structures are uncoupled. Illustratively, of all bit structures of the two-dimensional network layout, there is at least one coupling unit (where, for example, there are at least 3 bit structures), and one bit structure in the coupling unit is coupled with the other at least two bit structures.
To facilitate implementation of the solution in the examples of the present application by a person skilled in the art, the inventors have also proposed a method for constructing qubits with tunable frequencies and controllable tunable ranges (and correspondingly controllable tunable amplitudes).
The method comprises the following steps:
step S101, selecting adjacent first and second regions on the substrate.
Since the size of one substrate is generally limited, and the number of qubits therein is also desired to be configured more, and various reading and control lines are also required to be provided, it is more advantageous to plan and layout the configuration positions of various components in advance. Based on this, the spatial positions of the desired setting components, for example, the first region and the second region, are selected in advance.
Step S102, a qubit is manufactured and formed in a first area, and the qubit is provided by a first quantum circuit formed by connecting a first capacitor and a single Josephson junction in parallel.
And step S103, manufacturing a second quantum circuit formed by connecting a second capacitor and a direct current superconducting quantum interferometer in parallel in a second area, wherein the second quantum circuit is further coupled with the first quantum circuit.
Step S104, fabricating a transmission line on the substrate for adjusting the qubit frequency, wherein the transmission line is sufficiently close to the dc superconducting quantum interferometer to couple with each other, thereby allowing the transmission line to generate a magnetic field acting on the dc superconducting quantum interferometer under the excitation of the driving signal.
Fabrication of the various control lines and components provided by embodiments of the present application may require deposition of one or more materials, such as superconductors, dielectrics, and/or metals. Depending on the materials selected, these materials may be deposited using deposition processes such as chemical vapor deposition, physical vapor deposition (e.g., evaporation or Sputtering), or epitaxy techniques, as well as other deposition processes, including, for example, ion Beam Assisted Deposition (IBAD), vacuum Evaporation plating (evap), molecular Beam Epitaxy (MBE), pulsed Laser Deposition (PLD), chemical Vapor Deposition (CVD), sol-gel (sol-gel), and Magnetron 25Sputtering, among others.
And the traces and components described in embodiments of the present application may require removal of one or more materials from the device during the manufacturing process. The removal process may include, for example, a wet etching technique, a dry etching technique, or a lift-off (lift-off) process, depending on the material to be removed. The materials forming the circuit elements described herein may be patterned using known exposure (lithographic) techniques, such as photolithography or electron beam exposure.
Based on the above bit structure, an exemplary application example thereof may be a quantum bit or a quantum chip. Thus, it can be known that the quantum chip has a bit structure; similarly, a quantum computer has the aforementioned quantum chip, and correspondingly has the aforementioned bit structure.
It should be noted here that: the above quantum chip set in the quantum computer is similar to the structure in the above quantum chip embodiment and has the same advantageous effects as the above quantum chip embodiment, so that a detailed description is omitted. For technical details not disclosed in the embodiments of the quantum computer of the present application, those skilled in the art will understand with reference to the above description of the quantum chip, and for the sake of economy, the details are not repeated here. In various embodiments, during operation of a quantum computer, superconducting quantum circuits and/or superconducting classical circuits (such as various lines through which corresponding read, operation/control signals are applied to the quantum chip by a signal source), superconducting circuit elements are fabricated and used in a refrigeration device, such as a dilution refrigerator, to cool them to a temperature that allows their fabrication materials to exhibit superconducting properties.
Wherein the material is a superconducting material and is understood to be a material that exhibits superconducting properties below the critical temperature of superconduction. Examples of superconducting materials include aluminum (superconducting critical temperature of 1.2K) and niobium, indium, tantalum, and the like.
The embodiments described above by referring to the drawings are exemplary only and are not to be construed as limiting the present application.
For purposes of clarity, technical solutions, and advantages of embodiments of the present application, one or more embodiments will now be described with reference to the drawings, wherein like reference numerals are used to refer to like components throughout. In the previous description, for purposes of explanation, numerous specific details are set forth in order to provide a thorough understanding of one or more embodiments. It may be evident, however, that one or more embodiments may be practiced without these specific details, and that such embodiments may be incorporated by reference herein without departing from the scope of the claims.
It should be noted that the terms "first," "second," and the like in the description and claims of the present application and the above figures are used for distinguishing between similar objects and not necessarily for describing a particular sequential or chronological order. It is to be understood that the data so used may be interchanged where appropriate such that embodiments of the present application described herein may be implemented in sequences other than those illustrated or otherwise described herein. Furthermore, the terms "comprises," "comprising," and "having," and any variations thereof, are intended to cover a non-exclusive inclusion, such that a process, method, system, article, or apparatus that comprises a list of steps or elements is not necessarily limited to those steps or elements expressly listed but may include other steps or elements not expressly listed or inherent to such process, method, article, or apparatus.
The foregoing detailed description of the construction, features and advantages of the present application will be presented in terms of embodiments illustrated in the drawings, wherein the foregoing description is merely illustrative of preferred embodiments of the application, and the scope of the application is not limited to the embodiments illustrated in the drawings.
Claims (14)
1. A bit structure, comprising:
a qubit without a frequency adjustment structure, wherein the qubit is insensitive to a magnetic flux signal such that frequency tuning of the qubit is not responsive to a direct control signal, wherein the direct control signal is directly applied to the qubit by the magnetic flux signal and is implemented as a signal that operates in frequency; and
a frequency regulation circuit constructed based on a superconducting quantum interferometer, the frequency regulation circuit coupled without additional connection to the qubit, the frequency regulation circuit configured to operate the superconducting quantum interferometer with a magnetic field to implement frequency control of the qubit.
2. The bit structure of claim 1, wherein the bit structure further comprises: a read circuit coupled to the qubit and configured to perform a read operation on the qubit;
and/or driving a steering circuit coupled to the qubit and configured to perform a transition excitation operation on the qubit.
3. The bit structure of claim 1, wherein the superconducting quantum interferometer is a radio frequency superconducting quantum interferometer;
alternatively, the superconducting quantum interferometer is a direct current superconducting quantum interferometer and has two josephson junctions that are symmetrical.
4. A bit structure according to claim 1, 2 or 3, wherein the frequency modulation circuit has a capacitance and the superconducting quantum interferometer is shunted to the capacitance.
5. The bit architecture of claim 2 wherein the frequency regulation circuit has a frequency control element.
6. The bit structure of claim 5, wherein the frequency control element is a magnetic flux control line.
7. The bit structure according to claim 2, characterized in that the bit structure has one or more of the following definitions:
the first limit, drive the regulation and control circuit to be the microwave control line;
a second definition, the read circuit is a read resonator;
in a third definition, the read circuit, the drive regulation circuit, and the frequency regulation circuit are each coupled to the qubit through separate capacitors.
8. The bit structure of claim 1, wherein the qubit is comprised of a capacitor in parallel with a single josephson junction;
and/or the frequency regulating circuit is capacitively coupled with the qubit.
9. A multi-bit device comprising at least two bit structures according to any one of claims 1 to 8, wherein the at least two bit structures are arranged adjacent and coupled to each other.
10. The multi-bit device of claim 9, wherein the at least two bit structures are disposed adjacent to each other and are coupled to each other by an adjustable coupling structure, and wherein the adjustable coupling structure is provided by an adjustable qubit configured with a frequency signal line;
or all bit structures are in one-dimensional chained arrangement and are coupled in pairs in sequence;
alternatively, all bit structures are in a two-dimensional network layout and there is at least one coupling unit in which one bit structure is coupled with at least two other bit structures.
11. A quantum chip having a bit structure as claimed in any one of claims 1 to 8, or a multi-bit device as claimed in claim 9 or 10.
12. A quantum computer comprising the quantum chip of claim 11.
13. A method of making a quantum bit having a tunable frequency and a controllable tunable range, the method comprising:
selecting adjacent first and second regions on the substrate;
forming a qubit in a first area, wherein the qubit is provided by a first quantum circuit formed by connecting a first capacitor and a single Josephson junction in parallel;
manufacturing a second quantum circuit formed by connecting a second capacitor and a direct current superconducting quantum interferometer in parallel in a second area, wherein the second quantum circuit is also coupled with the first quantum circuit;
a transmission line is fabricated on the substrate that adjusts the qubit frequency, and the transmission lines are sufficiently adjacent to the dc superconducting quantum interferometers to couple to each other, thereby allowing the transmission lines to generate a magnetic field acting on the dc superconducting quantum interferometers under excitation by the drive signal.
14. The method of claim 13, wherein the direct current superconducting quantum interferometer comprises a superconducting loop and two josephson junctions in parallel, and the two josephson junctions are asymmetric.
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