CN116187461A - Bit structure, quantum chip, manufacturing method of quantum chip and quantum computer - Google Patents

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

A kind of bit structure, quantum chip and its manufacturing method and quantum computer

technical field

This application belongs to the field of quantum information, especially the field of quantum computing technology. In particular, this application relates to a bit structure, a quantum chip and its manufacturing method, and a quantum computer.

Background technique

The qubit located on the quantum chip is the basic unit for performing quantum computing. By adjusting the frequency of the qubit, the performance of the qubit can be adjusted to achieve a series of operations. Generally, a superconducting qubit has a capacitor and a superconducting quantum interferometer, and the maximum frequency of the qubit can be adjusted through the charging energy of the capacitor and the Josephson energy. Correspondingly, in order to control the frequency of the qubit, a DC bias line needs to be configured. However, the magnetic flux noise generated by the DC bias line will adversely interfere with the phase decoherence time of the qubit.

Contents of the invention

Examples of the present application provide a bit structure, a quantum chip, a manufacturing method thereof, and a quantum computer. While adjusting the frequency of the qubit, it can also reduce or even avoid the adverse interference caused by the frequency adjustment in the current qubit to the phase decoherence time of the qubit.

The solutions exemplified in this application are implemented in the following manner.

In the first aspect, the present application example proposes a bit structure. It includes:

Qubits without frequency tuning structure, qubits are insensitive to magnetic flux signals, so that the frequency tuning of qubits does not respond to direct control signals, wherein the direct control signals are directly applied to qubits by magnetic flux signals and implemented as signals for frequency manipulation ;as well as

A frequency control circuit constructed based on a superconducting quantum interferometer, the frequency control circuit is coupled to the qubit without additional connections, and the frequency control circuit is configured to use a magnetic field to operate the superconducting quantum interferometer to implement frequency control on the qubit.

In this bit structure, a frequency control circuit based on a superconducting quantum interferometer is used. Therefore, a flux control signal can be applied to the frequency control circuit, and then the frequency control circuit indirectly controls the frequency of the qubit. Therefore, the solution exemplified in the present application can avoid the magnetic flux noise existing in the direct frequency regulation of the qubits, and further alleviate the adverse effect on the coherence time of the qubits caused by the noise. In addition, since no additional connection is required between the frequency regulation circuit and the qubit, the process can be simplified to a certain extent—such as fewer configurations of various circuits, connection operations, etc.—thus reducing the difficulty of manufacturing and shortening the production cycle.

According to some examples of the present application, the bit structure further includes: a read circuit, coupled with the qubit and configured to perform a read operation on the qubit; and/or, a drive regulation circuit, coupled with the qubit and configured to perform a read operation on the qubit Bits implement transition excitation operations.

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 DC superconducting quantum interferometer, and has two symmetrical Josephson junctions.

According to some examples of the present application, the frequency regulation circuit has a capacitor, and the superconducting quantum interferometer is shunted with the capacitor.

According to some examples of the present application, the frequency regulation circuit has a frequency control element.

According to some examples of the present application, the frequency control element is a flux control wire.

According to some examples of the present application, the driving regulation 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, qubits are composed of capacitors connected in parallel with a single Josephson junction.

According to some examples of the present application, the qubit is composed of a capacitor connected in parallel with a single Josephson junction; and/or, the frequency regulation circuit is coupled with the qubit capacitor.

According to some examples of the present application, the readout circuit, the drive regulation circuit and the frequency regulation circuit are each coupled to the qubit through a capacitance.

In a second aspect, the present application exemplarily proposes a multi-bit device, which includes at least two aforementioned bit structures, and at least two bit structures are adjacently arranged and coupled to each other.

According to some examples of the present application, the above-mentioned at least two bit structures are arranged adjacent to each other and are coupled to each other through 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 chain layout, and are coupled in turn; or, all bit structures are in a two-dimensional network layout, and there is at least one coupling unit, and a bit structure in the coupling unit coupled with at least two other bit structures.

In the third aspect, the present application exemplarily proposes a quantum chip, which has the aforementioned bit structure.

In the fourth aspect, the present application exemplarily proposes a quantum computer, which includes the aforementioned quantum chip.

In the fifth aspect, the present application exemplifies a method for fabricating qubits with tunable frequency and controllable tunable range. The method includes:

selecting adjacent first and second regions on the substrate;

Fabricating and forming qubits in the first region, and the qubits are provided by a first quantum circuit composed of a first capacitance and a single Josephson junction in parallel;

Fabricating a second quantum circuit composed of a second capacitance and a DC superconducting quantum interferometer in parallel in the second region, and the second quantum circuit is also coupled to the first quantum circuit;

A transmission line for adjusting the qubit frequency is fabricated on the substrate, and the transmission lines are sufficiently close to the DC superconducting quantum interferometer to be coupled to 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.

According to some examples of the present application, the DC superconducting quantum interferometer includes a superconducting loop and two Josephson junctions connected in parallel, and the two Josephson junctions are asymmetric.

Beneficial effect:

Compared with the problem of shortening the bit coherence time caused by directly configuring the frequency control circuit for the qubit, in the example of this application, the frequency control circuit based on the superconducting quantum interferometer is used to pass the magnetic field applied to the superconducting quantum interferometer The signal controls the frequency of the qubit indirectly, so that the direct application of the magnetic field signal to the qubit can be avoided, thereby preventing the interference of the phase decoherence time of the qubit from being adversely affected.

Description of drawings

For a clearer description, the drawings that need to be used in the description will be briefly introduced below.

Fig. 1 is a schematic structural diagram of a qubit on a quantum chip in the related art;

Fig. 2 is the equivalent circuit diagram of the bit structure in the example of this application;

Fig. 3 is the numerical simulation diagram of the bit structure in the example of the present application;

FIG. 4 is an equivalent circuit diagram of coupling the bit structure in FIG. 2 through an adjustable coupler in the example of the present application.

Explanation of reference numerals: 100-bit structure; 101-basic bit; 102-adjustable structure; 103-reading structure.

Detailed ways

A quantum chip is a processor in a quantum computer that performs quantum calculations. The qubit structure contained in the quantum chip is the processing unit of the processor. A qubit is a two-level system that obeys the laws of quantum mechanics and can be in any superposition state of 0 and 1.

According to the different physical systems used to construct qubits, qubits include superconducting quantum circuits, semiconductor quantum dots, ion traps, diamond vacancies, topological quantum, photons, etc. in terms of physical implementation. Among them, superconducting quantum computing is currently the fastest and best solid-state quantum computing implementation.

The energy level structure of superconducting quantum circuits can be regulated by external electromagnetic signals, and the design and customization of the circuits are highly controllable. At the same time, thanks to the existing mature integrated circuit technology and micro-nano processing technology, superconducting quantum circuits have scalability and advantages that are difficult to match with other qubit physical systems.

Quantum chips based on superconducting quantum circuits include superconducting circuit structures such as qubits and microwave resonators. The qubit is a two-level system composed of a capacitor and a Josephson junction with nonlinear inductance characteristics. By designing into different shapes, different electrical parameter states such as capacitance and inductance can be achieved. Transmon qubit (transmission sub-qubit) is shaped like a "+", which consists of a cross-shaped capacitor and a superconducting quantum interference device (Superconducting Quantum Interference Device, referred to as squid) connected to the end of a branch of the capacitor. Among them, a superconducting quantum interference device (squid) includes one or more Josephson junctions; a Josephson junction is a device that includes two electrodes and a thin insulating barrier layer separating the two electrodes, and the two The material of the electrodes can exhibit superconducting properties at its own critical temperature or exhibit superconducting properties below this critical temperature property.

In the above-mentioned qubit system, there are various circuit structures with different functions around the qubits, for example, read resonant cavities and couplers for coupling connection between qubits.

The circuit structure also includes a drive control signal line (XY-ControlLine, also known as an xy control line or a pulse control signal line) for performing XY rotation operations on the qubits. A qubit can be excited by a transition by applying a driving voltage signal in the circuit; it is associated with the qubit through capacitive coupling.

The circuit structure also includes the circuit structure for Z-rotation operation on the qubit, and is completed by the control signal line near the superconducting quantum interference device (squid); it is called the flux control signal line (Z-Control Line, also known as Z control signal line or frequency regulation signal line). As mentioned above, the magnetic flux control signal line is arranged near the superconducting quantum interference device (squid), which excites current and is inductively coupled with the superconducting quantum interference device (squid) through a magnetic field.

It should be noted that both the flux control signal line and the drive control line can be used to control qubits, but their control forms and purposes are essentially different.

Wherein, the driving control signal line applies a pulse to the qubit in the form of an electric field, and the pulse makes the energy level of the qubit transition.

The signal transmitted by the magnetic flux regulation signal line will generate a magnetic field and apply it to the area of the superconducting quantum interference device (squid), and the magnetic flux passing through the area of the quantum interference device (squid) can cause the change of the critical current of the squid. The change of the critical current leads to the change of the frequency of the tunable qubit, that is, the frequency of the qubit can be controlled through the signal transmitted by the magnetic flux regulation signal line.

FIG. 1 is a schematic structural diagram of qubits arranged on a quantum chip in the related art.

As shown in FIG. 1 , the qubit structure often adopts a single capacitor to ground, and a superconducting quantum interference device with one end connected to the ground and the other end connected to the capacitor. And the capacitor is often a cross-shaped parallel plate capacitor.

As shown in Figure 1, the cross-shaped capacitor plate C _q (that is, the bit capacitor) is surrounded by the ground plane (GND), and there is a gap (usually an air gap, insulation) between the cross-shaped capacitor plate C _q and the ground plane (GND). .

One end of the superconducting quantum interference device is connected to the cross-shaped capacitive plate C _q (the end of one capacitive arm, such as the first end mentioned later), and the other end is connected to the ground plane (GND).

Since the first end of the cross-shaped capacitor plate C _q is usually used to connect to the superconducting quantum interference device, the second end is used to couple with the read resonant cavity. The other two ends of the cross-shaped capacitor plate C _q are used for coupling with adjacent qubits to realize bit expansion. A certain space is usually reserved near the first end and the second end for arranging microwave transmission lines such as drive control signal lines and magnetic flux control signal lines. Likewise, a certain space is usually reserved near the resonant cavity for arranging a read signal transmission line coupled with the resonant cavity.

When performing quantum computing, the frequency of the qubit is first adjusted to the working frequency (initial state production) by using the flux control signal on the flux control signal line, and then the quantum state control signal is applied to the quantum in the initial state through the drive control signal line. The quantum state of the bit is regulated, and then the resonant cavity is used to read the quantum state of the regulated qubit.

Specifically, a read detection signal (for example, a microwave signal with a frequency of 4GHz-8GHz) can be applied on the read signal transmission line coupled with the resonator, and then the read feedback signal output through the read signal transmission line (in response to Read the signal of the detection signal) and analyze it to determine the quantum state that the qubit is in. The structure of the magnetic flux control signal line, the drive control signal line and the read signal transmission line can all adopt the microwave transmission line structure, which will not be repeated here.

It should be noted that the quantum chip performs the quantum calculation process as follows:

Send the waveform instructions generated by compiling the quantum program in the quantum computing task to the physical signal generation device. The physical signal generating means generates corresponding physical signals, which are sent to the quantum chip to operate the corresponding qubits. Then, apply the quantum state reading signal to the corresponding qubit, and determine the quantum state information of the qubit according to the reading feedback signal fed back by the qubit based on the quantum state reading signal, and finally analyze the quantum calculation result.

As mentioned above, the calculation process of the qubit needs to control the qubit—such as frequency regulation—and it is generally implemented through the frequency regulation signal line. As far as the inventors of the present application know, common superconducting qubits are generally composed of SQUIDs shunted by capacitance. The SQUID is generally a symmetric Josephson junction, and thus can generate a frequency-tunable superconducting qubit. By controlling any one or both of the capacitor charging energy and the Josephson energy, the maximum frequency of the bit can be regulated; by controlling the asymmetry of the SQUID, the adjustable range of the bit frequency can be adjusted. However, the SQUID with a higher degree of asymmetry has high requirements for its manufacturing process. For example, if the adjustable range of the bit frequency is designed to be 100 MHz, it is required to use a SQUID with a higher asymmetry, but the SQUID with a higher asymmetry will have greater difficulty in process implementation.

Therefore, based on the special requirements of the bit frequency adjustable range and the consideration of reducing the difficulty of process realization, a new qubit structure can be constructed; it is also a small-range frequency adjustable bit. In general, the new qubit structure adds an adjustment control structure on the basis of a fixed bit frequency (referring to no Z control signal line), so as to realize the regulation of the fixed bit frequency (and the adjustable range is controllable).

Further, the above-mentioned solution realized can also obtain advantages in other aspects. For example, since the bit without the Z control signal line is designed, there will be no interference on the phase decoherence time of the bit by magnetic flux noise generated if the Z control signal line is used.

FIG. 2 is an equivalent circuit diagram of the bit structure in the example of the present application. As shown in FIG. 2 , in this bit structure, the bit part (referred to as the basic bit 101 for ease of description and distinction) is a capacitor (marked as C _q in the figure) and a single Josephson junction (marked as JJ) in parallel, and usually a superconducting connection.

The basic bit 101 is insensitive to the magnetic flux signal, so that the frequency change of the qubit cannot be realized by directly controlling the signal. Moreover, the direct control signal is directly applied to the qubit by the magnetic flux signal and implemented as a frequency operation. In other words, if the frequency of the fundamental bit is to be adjusted, it cannot be achieved by directly applying a magnetic flux signal to the fundamental bit. For example, if you try to configure a Z line for the basic bit, and then apply a DC driving signal to the Z line to excite it, and then use the direct control signal generated by the excited Z line to manipulate the frequency of the basic bit, it will not achieve the goal. Therefore, the base bits 101 can generally be described as non-tuning bits.

Meanwhile, the basic bit 101 has a separate XY control line (marked as Xcontrol in the figure), and the two are capacitively coupled.

Further, the basic bit 101 is connected/capacitively coupled with the tunable structure 102 (for example, marked as Tunable in the partial diagram) through the capacitance C _qt ; and there is no additional connection between the basic bit 101 and the tunable structure 102 (for example, both One or more electrodes are not shared, wherein the electrodes are, for example, capacitive electrodes having a capacitance to ground) ground-coupled.

The adjustable structure 102 is composed of a parallel SQUID shunted by a capacitor C _t (marked as two JJ loops in the figure). The adjustable structure 102 can be considered as an adjustable bit. , the basic bit 101 and the adjustable circuit 102 cooperate with each other to form a tunable bit.

And the adjustable structure 102 has a single Z control line (no separate XY control line). In order to read the bit structure 101 , its read part (read structure 103 ) is connected/capacitively coupled to the read cavity by the basic bit 101 through C _qr . In the example of FIG. 2 , the reading structure 103 is composed of a coplanar waveguide resonator and a capacitor connected in parallel.

Therefore, in some examples, a bit structure is proposed, which includes: a qubit and a frequency regulation circuit. The qubits therein have no frequency adjustment structure (that is, no Z control line, for example marked as Zcontrol). Moreover, the frequency regulation circuit is constructed based on a superconducting quantum interferometer. A frequency regulation circuit is coupled to the qubit without additional connections, the frequency regulation circuit being configured to perform frequency control on the qubit by operating the superconducting quantum interferometer with a magnetic field.

The superconducting quantum interferometer can be, for example, a radio frequency superconducting quantum interferometer, or it can also be a direct current superconducting quantum interferometer. The DC superconducting quantum interferometer can directly use the magnetic flux control circuit to realize the adjustment of the frequency. The RF superconducting quantum interferometer can be coupled with the resonant circuit through mutual inductance; where the resonant circuit is driven by RF current through RF.

For a DC superconducting quantum interferometer, it has two Josephson junctions, which can optionally be configured symmetrically in a different example. Alternatively, optionally configured as an asymmetrical two Josephson junctions, allowing control over the frequency tuning range.

The frequency control circuit can also be configured with a capacitor, and based on this, in the frequency control circuit, the superconducting quantum interferometer is shunted with the capacitor. Further, the frequency control circuit can also be configured with a frequency control element so as to direct current superconducting quantum interferometer (DC-SQUID). Among them, the frequency control element is, for example, a flux control line. In order to realize the correlation/signal coordination between the adjustable structure and the basic bits, for example, the adjustable structure may use the capacitance C _qt to realize capacitive coupling with the basic bits.

In order to realize the reading of the result of performing quantum calculation on the new bit structure, it is further possible to configure a reading structure/reading circuit in the bit structure so as to perform a reading operation on the qubits. The readout circuit is, for example, a readout resonator. Further, a capacitor connected in parallel with the read resonator may also be configured in the read circuit. On this basis, the reading circuit realizes capacitive coupling with the basic bit through the capacitance C _qr .

Similarly, in order to operate qubits such as Z-rotation, a driving control circuit may be configured in the bit structure so as to be configured to perform a transition excitation operation on the qubits. For example, the driving control circuit is a microwave control line (XY control line, for example marked as xcontrol), which can achieve capacitive coupling with the basic bits through a capacitor.

In the bit structure, various lines and components therein can be various appropriately selected transmission lines, such as coplanar waveguide transmission lines. In the system of superconducting quantum computers, the materials of these circuits and components can be made of materials that exhibit superconducting properties at temperatures at or below the critical temperature, such as at about 10-100 millikelvin (mK) or about 4K. Superconductor materials—such as aluminum, niobium, tantalum or titanium nitride, etc.; the superconductor materials are not limited to the ones listed above, and materials that exhibit superconducting properties at temperatures equal to or lower than the critical temperature can be selected according to need to use.

Among them, Josephson junctions are, for example, tunnel junctions, point contacts and various microbridges. Various circuits and components can be selected to be fabricated on one or more surfaces of single-layer substrates, double-layer substrates or multi-layer substrates (substrates or described as substrates/bases), and can even be partially or completely located on the surface of the substrate the following. As a specific and alternative example, the material of the substrate is, for example, sapphire or high-resistance silicon material.

In the structure shown in FIG. 2 , compared with the general qubit, the bit structure 100 is additionally configured with a control structure/adjustable structure 102 ; and the adjustable structure is coupled with the basic bit 101 through capacitive coupling. Wherein, the coupling between the control structure and the basic bits can be configured as dispersive coupling, so as to avoid direct energy exchange between the two. In order to achieve dispersion coupling, the detuning amount between the frequency of the basic bit and the frequency of the adjustable structure can be selected (the frequency of the basic bit is greater than the frequency of the adjustable structure) to be much greater than the coupling strength between the two, that is, the following formula 1:

Δ>>g

Among them, Δ is the detuning amount between the basic bit and the adjustable structure, and g is the coupling strength between the basic bit and the adjustable structure.

The frequency of the bit structure 100 is the frequency exhibited after the bit frequency ω _q of the basic bit 101 is affected by the adjustable structure 102 . As mentioned above, the adjustable structure 102 can be described as a qubit functionally, therefore, its bit frequency is ω _t , and no separate XY control line is set, and it is always in the |0> state by default. Considering the dispersion coupling of fixed frequency bit/basic bit and adjustable structure, the resonant frequency of fixed bit frequency can be modified as follows:

ω′ _q = ω _q -χ

Δ＝ω _q -ω _t

Since the basic bit 101 in the bit structure 100 has only a single XY control line, but the basic bit does not have a single Z control line, the function analog of the Z control line is configured to the adjustable structure. Therefore, the direct interference of the magnetic flux noise of the Z control line on the frequency of the basic bit can be avoided, and the phase decoherence time of the bit is greatly improved.

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 the flux noise of the Z control line will have little modification/influence on the frequency of the bit structure 100 . And the degree of influence is much smaller than the direct influence on the bit frequency of directly configuring the Z control line independently. Therefore, it can be considered that the introduction of the adjustable structure can greatly reduce the influence of the magnetic flux noise of the Z control line on the bit phase decoherence time. In addition, the weak tunability of the bit frequency can be realized by controlling the dispersion coupling strength between the bit and the tunable structure and the frequency of the tunable structure.

In order to verify the above structure, numerical simulation is now carried out:

The bit capacitance and the shunt capacitance of the frequency regulation circuit are 88fF, and the coupling capacitance between the basic bit and the adjustable structure is 10fF. The critical current of the Josephson junction of the basic bit is about 38nA; the critical current of the Josephson junction of the adjustable structure SQUID is about 15nA.

Through numerical simulation (as shown in FIG. 3 ), the bit structure 100 is adjustable between approximately 5.38GHz˜5.51GHz, and the adjustable range is 134MHz. The range can be further adjusted to make the adjustable range larger. At the same time, it can be seen that most areas in the entire adjustment period satisfy the dispersion coupling condition, and when the magnetic flux bias is 0, the frequency of the adjustable structure is the largest, and the detuning amount is the smallest at this time, and the dispersion condition is weak.

Based on the above description, it can be understood that the bit structure can achieve slightly adjustable bit frequency based on the existing technology level of micro-nano processing technology, and the adjustable amplitude (adjustable range) is also controllable; that is, it can be controlled by operation By adjusting the structure, qubits with different tunable ranges can be obtained. That is to say, as far as the inventors of the present application know, once the existing qubits with adjustable frequency range are manufactured, their frequency adjustable range is fixed, and cannot be adjusted as required during the use of qubits. Adjustment; however, through the solution illustrated in this application, it can be realized that after the bit is produced, it can be controlled according to needs to obtain different frequency adjustable ranges.

In particular, since the basic bit itself does not have an independent Z control line, and on the other hand, the Z control line is configured on an adjustable structure, so the phase decoherence time of the bit structure can be maintained at a relatively good level.

For the reading process of the bit structure, reference may be made to the reading of the traditional transmon (transmon) type superconducting qubit. Considering that the adjustable range of the frequency of the bit structure is relatively small, more accurate measurement can be considered in the process of testing the modulation spectrum of the bit structure.

In addition, in order to achieve a larger scale of quantum integration, multiple aforementioned bit structures can be selected to be coupled and integrated; for example, at least two bit structures are arranged adjacently and coupled to each other. In some examples, an adjustable coupler can be used to realize the coupling connection of two bit structures, please refer to Figure 4; in other examples, a non-adjustable coupler can also be selected as the coupler. The adjustable coupler can be provided by an adjustable qubit configured with a frequency signal line.

In FIG. 4, Coupler represents an adjustable coupler; it is used to adjust the coupling strength between the first bit structure (Qubit1) and the second bit structure (Qubit2), so that the coupling strength between the two bits reaches an open ( can reach the set coupling strength) and off state. Qubit1 and Qubit2 are coupled to each other through a capacitor (C ₃₇ ), and are also coupled to an adjustable coupler through capacitors (C ₃₄ , C ₄₇ ), respectively.

In Fig. 4, the two Josephson junctions of the superconducting quantum interferometer in the copuler are configured as symmetric junctions; however, as a beneficial attempt, the aforementioned two Josephson junctions are preferably configured as asymmetric junctions; based on asymmetric Symmetric junctions enable weakly tunable structures. Therefore, the DC superconducting quantum interferometer includes a superconducting loop and two Josephson junctions connected in parallel, and the two Josephson junctions are asymmetric; usually it is shown that the areas of the two Josephson junctions are different, and in the circuit It is reflected that the critical current of the two is different.

In other words, in the structure of FIG. 4 , the adjustable coupler is the same as the adjustable structure in FIG. 2 (in other examples, it can also be adjusted to couplers of other structures). However, it is also possible to replace the adjustable coupler by a weakly adjustable structure. And, accordingly, set a reasonable coupling capacitance between the bit and the Coupler (considering reducing the frequency difference between the turn-on and turn-off points of the adjustable coupling), and set the turn-on and turn-off points to weakly adjustable structure frequencies The two flux insensitive points.

In the open position, the frequency of the coupler has a large effect on the effective coupling strength between the two bits. A slight change in the frequency of the coupler at this position may result in a large change in the effective coupling strength between the two bits. And the two-bit gate requires relatively stable effective coupling strength, therefore, it is necessary to set the frequency of the coupler when the coupler performs two-bit coupling to open at the magnetic flux insensitive point. In this way, it can not only reduce the difficulty of the tester in measuring the effective coupling strength during the test (traditional adjustable couplers may not be able to find the position where the coupling is turned on during actual use), but also provide stable for two-bit gate operation. Coupling turns on the frequency position.

When configuring more bit structures, these bit structures can adopt a one-dimensional chain layout, or a two-dimensional network layout. In an example of a one-dimensional chain layout, all bit structures may be associated with each other in a sequential pairwise coupling manner—a one-dimensional chain may be formed. Alternatively, in the structure of the one-dimensional chain layout, some bit structures are coupled to each other, while other bits may not be coupled to each other. Similarly, in the scheme of two-dimensional network layout, all the bit structures may be associated with each other, that is, coupled, or partially coupled and even the remaining bit structures are not coupled. Exemplarily, in all the bit structures of the two-dimensional network layout, there is at least one coupling unit (for example, there are at least 3 bit structures), and one bit structure in the coupling unit is coupled to at least two other bit structures.

In order to make it easier for those skilled in the art to implement the solutions in the examples of the present application, the inventor also proposed a method for constructing qubits with tunable frequency and controllable tunable range (correspondingly, the adjustable amplitude is also controllable). method.

The method includes the following steps:

Step S101 , selecting adjacent first and second regions on the substrate.

Since the size of a substrate is usually limited, and the number of qubits is expected to be more configured, and various read and control circuits need to be set, it will be more convenient to plan and lay out the configuration positions of various components in advance. is favorable. Based on this, the spatial positions where components are expected to be placed, such as the first area and the second area, are pre-selected.

Step S102 , fabrication and formation of qubits in the first region, and the qubits are provided by a first quantum circuit composed of a parallel connection of a first capacitor and a single Josephson junction.

Step S103 , fabricate a second quantum circuit in the second region, which is composed of a second capacitor and a DC superconducting quantum interferometer connected in parallel, and the second quantum circuit is also coupled to the first quantum circuit.

Step S104, fabricate a transmission line on the substrate for adjusting the frequency of the qubit, and the transmission lines are sufficiently close to the DC superconducting quantum interferometer to be coupled to 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.

The manufacture of various control lines and components provided in the 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 can be deposited using deposition techniques such as chemical vapor deposition, physical vapor deposition (e.g., evaporation or sputtering), or epitaxy, among other deposition techniques, including, for example, ion beam assisted deposition (IBAD), vacuum evaporation coating (Evaporation), molecular beam epitaxy (MBE), pulsed laser deposition (PLD), chemical vapor deposition (CVD), sol-gel (sol-gel) and magnetron sputtering Coating method (Magnetron 25 Sputtering), etc.

And the circuits and components described in the embodiments of the present application may require one or more materials to be removed from the device during the manufacturing process. Depending on the material to be removed, the removal process may include, for example, a wet etch technique, a dry etch technique, or a lift-off process. The materials forming the circuit elements described herein can be patterned using known lithographic techniques (eg, photolithography or electron beam exposure).

Based on the above-mentioned bit structure, an exemplary application example thereof may be a qubit or a quantum chip. Therefore, it can be known that a quantum chip has a bit structure; similarly, a quantum computer has the aforementioned quantum chip and correspondingly has the aforementioned bit structure.

What needs to be pointed out here is that the above quantum chip set in the quantum computer has a similar structure to the above quantum chip embodiment, and has the same beneficial effect as the above quantum chip embodiment, so it will not be repeated here. For the technical details not disclosed in the quantum computer embodiments of this application, those skilled in the art should refer to the description of the quantum chip above for understanding, and to save space, details are not repeated here. In various embodiments, during the operation of the quantum computer, superconducting quantum circuits and/or superconducting classical circuits (such as various superconducting classical circuits) are fabricated and used to apply corresponding read, operation/control signals to the quantum chip through signal sources wires), superconducting circuit components in refrigeration equipment such as dilution refrigerators to cool them to temperatures that allow the material from which they are made to exhibit superconducting properties.

The material therein is a superconducting material, and can be understood as a material exhibiting superconducting properties below the superconducting critical temperature. 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, and are only for explaining the present application, and cannot be construed as limiting the present application.

To make the purposes, technical solutions, and advantages of the embodiments of the present application clearer, one or more embodiments will now be described with reference to the accompanying drawings, wherein like reference numerals are used to refer to like components throughout. In the foregoing description, for purposes of explanation, numerous specific details were set forth in order to provide a thorough understanding of one or more embodiments. It may be evident, however, that in various instances, one or more embodiments may be practiced without these specific details, and that various embodiments may be incorporated by reference to each other where not inconsistent.

It should be noted that the terms "first" and "second" in the description and claims of the present application and the above drawings are used to distinguish similar objects, but not necessarily used to describe a specific sequence or sequence. It is to be understood that the data so used are interchangeable under appropriate circumstances such that the embodiments of the application described herein can be practiced in sequences other than those illustrated or described herein. Furthermore, the terms "comprising" and "having", as well as any variations thereof, are intended to cover a non-exclusive inclusion, for example, a process, method, system, product or device comprising a sequence of steps or elements is not necessarily limited to the expressly listed instead, may include other steps or elements not explicitly listed or inherent to the process, method, product or apparatus.

The structure, features and effects of the application have been described in detail above based on the embodiments shown in the drawings. The above descriptions are only preferred embodiments of the application, but the application does not limit the scope of implementation as shown in the drawings. Changes made to the idea of the application, or modifications to equivalent embodiments that are equivalent to changes, and still within the spirit covered by the description and illustrations, shall be within the scope of protection of the application.

Claims (14)

1. A bit structure, characterized in that, comprising: A qubit without a frequency tuning 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 applied directly to the qubit by the magnetic flux signal and implemented as a signal for frequency manipulation; and A frequency control circuit constructed based on a superconducting quantum interferometer, the frequency control circuit is coupled to the qubit without additional connections, and the frequency control circuit is configured to use a magnetic field to operate the superconducting quantum interferometer to implement frequency control on the qubit. 2. The bit structure according to claim 1, wherein the bit structure further comprises: a readout circuit, coupled with the qubit and configured to perform a read operation on the qubit; And/or, the driving control circuit is coupled with the qubit and configured to perform a transition excitation operation on the qubit. 3. The bit structure according to claim 1, wherein the superconducting quantum interferometer is a radio frequency superconducting quantum interferometer; Or, the superconducting quantum interferometer is a DC superconducting quantum interferometer, and has two symmetrical Josephson junctions. 4. The bit structure according to claim 1, 2 or 3, wherein the frequency control circuit has a capacitor, and the superconducting quantum interferometer is shunted with the capacitor. 5. The bit structure as claimed in claim 2, characterized in that the frequency control circuit has a frequency control element. 6. Bit structure according to claim 5, characterized in that the frequency control element is a flux control line. 7. The bit structure according to claim 2, characterized in that the bit structure has one or more of the following limitations: The first limitation is that the drive control circuit is a microwave control line; Second definition, the reading circuit is a reading resonator; The third limitation is that the reading circuit, the drive regulation circuit and the frequency regulation circuit are coupled to the qubit through independent capacitors. 8. The bit structure according to claim 1, wherein the qubit is composed of a capacitor connected in parallel with a single Josephson junction; And/or, the frequency regulation circuit is capacitively coupled with the qubit. 9. A multi-bit device, characterized in that it comprises at least two bit structures according to any one of claims 1 to 8, and at least two bit structures are adjacently arranged and coupled to each other. 10. The multi-bit device according to claim 9, characterized in that, the at least two bit structures are adjacent to each other and are coupled to each other through an adjustable coupling structure, and the adjustable coupling structure is configured by a frequency signal line Provided by tunable qubits; Or, all the bit structures are in a one-dimensional chain layout, and are coupled in turn; Alternatively, all the 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, characterized in that it has the bit structure as claimed in any one of claims 1 to 8, or the multi-bit device as claimed in claim 9 or 10. 12. A quantum computer, comprising the quantum chip according to claim 11. 13. A method for making qubits with tunable frequency and controllable tunable range, characterized in that the method comprises: selecting adjacent first and second regions on the substrate; Fabricating and forming qubits in the first region, and the qubits are provided by a first quantum circuit composed of a parallel connection of a first capacitor and a single Josephson junction; Fabricating a second quantum circuit composed of a second capacitance and a DC superconducting quantum interferometer in parallel in the second region, and the second quantum circuit is also coupled to the first quantum circuit; A transmission line for adjusting the qubit frequency is fabricated on the substrate, and the transmission lines are sufficiently close to the DC superconducting quantum interferometer to be coupled to 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. 14. The method according to claim 13, wherein the DC superconducting quantum interferometer comprises a superconducting loop and two Josephson junctions connected in parallel, and the two Josephson junctions are asymmetric.

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