Frequency shift of quantum computing devices

Abstract

According to one embodiment, an apparatus for frequency shifting of quantum computing elements includes a plurality of persistent current loops, each persistent current loop being couplable to a corresponding quantum computing element, a first plurality of signal lines, each persistent current loop being coupled to a corresponding signal line of the first plurality of signal lines, and a second plurality of signal lines, each persistent current loop being coupled to a corresponding signal line of the second plurality of signal lines, each persistent current loop being configured to induce a persistent current in the persistent current loop in response to a pulse in a corresponding signal line of the first plurality of signal lines and / or a corresponding signal line of the second plurality of signal lines, the persistent current being configured to cause a shift in the frequency of the corresponding quantum computing element.

Description

[Technical field]

[0001] The present disclosure relates to quantum computing, and more particularly to an apparatus for frequency shifting of quantum computing elements and a quantum computing system. [Background technology]

[0002] As the number of qubits increases, the requirement to fine-tune the direct current (DC) flux per qubit requires an increasing number of cables and equipment, which contributes to the system complexity and cost in several ways. DC wires can also limit the coherence time of the qubits and introduce low-frequency noise that causes drift. One option is to focus on the DC source design. However, controlling, for example, 2500 qubits or couplers is a complex task regardless of the type of DC source available. Mechanical or semiconductor switches with various temperature stages can be utilized, but they all have their drawbacks. Summary of the Invention [Means for solving the problem]

[0003] This Summary is provided to introduce a selection of concepts in a simplified form that are further described below in the Detailed Description. This Summary is not intended to identify key features or essential features of the claimed subject matter, nor is it intended to be used to limit the scope of the claimed subject matter.

[0004] It is an object to provide an apparatus for frequency shifting of quantum computing elements and a quantum computing system. These and other objects are achieved by the features of the independent claims. Further implementations are evident from the dependent claims, the description and the figures.

[0005] According to a first embodiment, an apparatus for frequency shifting of a quantum computing element includes a plurality of persistent current loops, each of which includes at least one Josephson junction, at least one shunt resistive element, and at least one inductive element, each of which can be coupled to a corresponding quantum computing element, a first plurality of signal lines, each of which is coupled to a corresponding one of the first plurality of signal lines, and a second plurality of signal lines, each of which is coupled to a corresponding one of the second plurality of signal lines, each of which is configured to induce a persistent current in the persistent current loop in response to a pulse in the corresponding one of the first plurality of signal lines and / or the corresponding one of the second plurality of signal lines, the persistent current being configured to cause a shift in the frequency of the corresponding quantum computing element. This apparatus can, for example, shift the frequency of the quantum computing element with a reduced number of required signal lines and / or signal sources.

[0006] In one implementation of the first aspect, each persistent current loop of the plurality of persistent current loops is electrically coupled to a corresponding signal line of the first plurality of signal lines and a corresponding signal line of the second plurality of signal lines, and is configured to induce a persistent current in the persistent current loop through at least one Josephson junction in response to a current between the corresponding signal line of the first plurality of signal lines and the corresponding signal line of the second plurality of signal lines exceeding a critical current of the at least one Josephson junction. The apparatus can, for example, shift the frequency of a quantum computing device with a reduced number of required signal lines and / or signal sources.

[0007] In another implementation of the first aspect, each persistent current loop is electrically coupled to a corresponding signal line of the first plurality of signal lines via at least one first coupling resistive element and / or at least one first coupling inductive element, and each persistent current loop is coupled to a corresponding signal line of the second plurality of signal lines via at least one second coupling resistive element and / or at least one second coupling inductive element. The coupling resistive element and / or the coupling inductive element can, for example, limit the flow of reverse current to non-addressed persistent current loops.

[0008] In another implementation of the first aspect, each persistent current loop of the plurality of persistent current loops is inductively coupled to a corresponding signal line of the first plurality of signal lines and a corresponding signal line of the second plurality of signal lines, and configured to induce a persistent current in the persistent current loop in response to a first pulse in the corresponding signal line of the first plurality of signal lines and a second pulse in the corresponding signal line of the second plurality of signal lines when a total induced current due to the first pulse and the second pulse in the persistent current loop is greater than a critical current of at least one Josephson junction of the persistent current loop. This apparatus can, for example, shift the frequency of a quantum computing device while reducing the number of required signal lines and / or signal sources.

[0009] In another implementation of the first aspect, each persistent current loop of the plurality of persistent current loops is inductively coupled to a corresponding quantum computing element and configured to cause a shift in frequency of the corresponding quantum computing element via a magnetic field induced by the persistent current. The apparatus can, for example, efficiently shift the frequency of the corresponding quantum computing element via a magnetic field induced by the persistent current.

[0010] In another implementation of the first aspect, each quantum computing element includes at least one Josephson junction, and the magnetic field is configured to adjust a Josephson inductance of the at least one Josephson junction of the corresponding quantum computing element. The apparatus can, for example, efficiently shift a frequency of the corresponding quantum computing element by adjusting the Josephson inductance of the at least one Josephson junction of the corresponding quantum computing element.

[0011] In another implementation of the first aspect, each quantum computing element includes a qubit or a coupler between qubits.

[0012] According to a second aspect, a quantum computing system includes a plurality of qubits and an apparatus according to the first aspect, where at least one persistent current loop of the plurality of persistent current loops of the apparatus is coupled to a corresponding qubit of the plurality of qubits. The apparatus can, for example, fine-tune the frequency of the qubit via the persistent current. Thus, no continuous external current is required for fine-tuning.

[0013] In one implementation of the second aspect, the quantum computing system further includes a plurality of couplers, each of which is coupled to two qubits of the plurality of qubits and configured to control the coupling between the two qubits, and at least one of the plurality of persistent current loops of the device is coupled to a corresponding coupler of the plurality of couplers. The device can, for example, fine-tune the frequency of the coupler through the persistent current. Thus, no continuous external current is required for fine-tuning.

[0014] In another implementation of the second aspect, each qubit of the plurality of qubits includes at least one Josephson junction and / or each coupler of the plurality of couplers includes at least one Josephson junction.

[0015] In another implementation of the second aspect, the plurality of qubits includes superconducting qubits.

[0016] In another implementation of the second aspect, the quantum computing system further includes a control unit coupled to the first and second signal lines of the device and configured to shift a frequency of a target quantum bit of the plurality of quantum bits by providing a pulse to one of the first signal lines corresponding to the target quantum bit and / or one of the second signal lines corresponding to the target quantum bit. The system can, for example, efficiently fine-tune the frequency of the target quantum bit.

[0017] Many of the attendant features will be more readily appreciated as the same becomes better understood by reference to the following detailed description considered in conjunction with the accompanying drawings, in which:

[0018] In the following, exemplary embodiments are explained in more detail with reference to the accompanying figures and drawings. [Brief description of the drawings]

[0019] [Figure 1] FIG. 1 is a schematic diagram illustrating an apparatus for frequency shifting of a quantum computing device according to one embodiment. [Diagram 2] FIG. 2 is a schematic diagram illustrating an apparatus for frequency shifting of a quantum computing device according to another embodiment. [Diagram 3] FIG. 2 is a schematic diagram illustrating an apparatus for frequency shifting of a quantum computing device according to another embodiment. [Figure 4] FIG. 2 is a schematic diagram illustrating a coupling between a persistent current loop and a quantum computing device according to one embodiment. [Diagram 5] 11 is a plot representation showing a simulation of current in different persistent current loops according to one embodiment. [Figure 6]1 is a plot representation showing a simulation of the current through the Josephson junctions of each persistent current loop. [Figure 7] 1 is a plot representation showing a simulation of the current flowing through the resistive element of each persistent current loop. [Figure 8] 1 is a plot representation showing a simulation of the current flowing in a persistent current loop for different pulse lengths. [Figure 9] 1 is a plot representation showing a simulation of the current through a resistive element of an addressed persistent current loop. [Figure 10] 1 is a plot representation showing a simulation of the current flowing in the persistent current loops as persistent current is applied and removed from one persistent current loop. [Figure 11] FIG. 11 is a schematic diagram illustrating a quantum computing system 1100 according to one embodiment. [Figure 12] FIG. 2 is a schematic diagram illustrating a control unit according to one embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0020] In the following, like reference numerals are used to denote like parts in the accompanying drawings.

[0021] In the following description, reference is made to the accompanying drawings which form a part hereof, and in which is shown by way of illustration specific embodiments in which the present disclosure may be arranged. It is to be understood that other embodiments may be utilized and structural or logical changes may be made without departing from the scope of the present disclosure. Therefore, the following detailed description is not to be taken in a limiting sense, and the scope of the present disclosure is defined by the appended claims.

[0022] For example, it should be understood that disclosure related to a described method may also apply to a corresponding device or system configured to perform that method, and vice versa. For example, where certain method steps are described, the corresponding device may include units that perform the described method steps, even if such units are not explicitly described or shown in the figures. Conversely, for example, where a particular apparatus is described in terms of functional units, the corresponding method may include steps that perform the described functions, even if such steps are not explicitly described or shown in the figures. Furthermore, it should be understood that features of the various exemplary aspects described herein may be combined with each other, unless otherwise specified.

[0023] FIG. 1 shows a schematic diagram of an apparatus 100 for frequency shifting of a quantum computing device according to one embodiment.

[0024] According to one embodiment, an apparatus 100 for frequency shifting of a quantum computing element includes a plurality of persistent current loops 101, each of which includes at least one Josephson junction 102, at least one shunt resistive element 201, and at least one inductive element 103, and each persistent current loop 101 is capable of being coupled to a corresponding quantum computing element.

[0025] Quantum computing elements may include, for example, qubits or couplers between qubits.

[0026] The apparatus 100 may further include a first plurality of signal lines 105, with each persistent current loop 101 of the plurality of persistent current loops being coupled at 110 to a corresponding signal line of the first plurality of signal lines 105.

[0027] Each persistent current loop 101 may be electromagnetically coupled at 110 to a corresponding signal line of the first plurality of signal lines 105. For example, each persistent current loop may be galvanically coupled to a corresponding signal line of the first plurality of signal lines 105. Thus, a current may flow from the corresponding signal line to the persistent current loop. Alternatively, each persistent current loop may be inductively and / or capacitively coupled to the corresponding signal line of the first plurality of signal lines 105. Thus, there may be electromagnetic interaction between the persistent current loop and the signal line even if no current flows.

[0028] The apparatus 100 may further include a second plurality of signal lines 106, with each persistent current loop 101 of the plurality of persistent current loops being coupled at 111 to a corresponding signal line of the second plurality of signal lines 106.

[0029] Each persistent current loop 101 may be electromagnetically coupled at 111 to a corresponding signal line of the second plurality of signal lines 106. For example, each persistent current loop may be galvanically coupled to a corresponding signal line of the second plurality of signal lines 106. Thus, a current may flow from the corresponding signal line to the persistent current loop. Alternatively, each persistent current loop may be inductively and / or capacitively coupled to a corresponding signal line of the second plurality of signal lines 106. Thus, there may be electromagnetic interaction between the persistent current loop and the signal line even if no current flows.

[0030] The first plurality of signal lines 105 and the second plurality of signal lines 106 may form a matrix. The first plurality of signal lines 105 may correspond to rows of the matrix and the second plurality of signal lines 106 may correspond to columns of the matrix, or vice versa.

[0031] Each persistent current loop 101 of the plurality of persistent current loops may be configured to induce a persistent current therein in response to a pulse in a corresponding signal line of the first plurality of signal lines 105 and / or a corresponding signal line of the second plurality of signal lines 106, the persistent current being configured to cause a shift in the frequency of a corresponding quantum computing element.

[0032] Each persistent current loop 101 may be coupled to a corresponding quantum computing element in various ways. For example, each persistent current loop 101 may be electrically connected to an inductive element for coupling the persistent current loop to the quantum computing element. The inductive element may be configured to shift the frequency of the corresponding quantum computing element by inducing a magnetic flux through the quantum computing element.

[0033] Each persistent current loop can be addressed by driving a pulse on a corresponding signal line in the first plurality of signal lines 105 and / or the second plurality of signal lines. The persistent current loop to which the persistent current is applied may be referred to as the addressed persistent current loop, the target persistent current loop, etc. Other signal lines in the first plurality of signal lines 105 and / or the second plurality of signal lines 106 may, for example, be floating during addressing. When a signal line is floating, there may be no electrical connection through which a current can flow. Thus, the persistent current is applied only to the addressed persistent current loop.

[0034] In this specification, the persistent current may refer to the effect that a persistent current is accumulated in the persistent current loop 101 by biasing the shunted Josephson junction above the critical current. The shunted Josephson junction refers to the persistent current loop including the shunt resistance element 201. The shunt resistance element 201 may also be called a shunt resistor or the like. The shunt resistance element 201 may stabilize a transient phenomenon in the persistent current loop 101. Thus, the shunt resistance element 201 may enable the persistent current loop 101 to controllably accumulate a persistent current in the inductive element 103 and the Josephson junction 102 for a steady state, even if no current flows through the shunt resistance element 201 at the steady state.

[0035] The persistent current can be added to each persistent current loop 101 as a discrete flux quantum because the magnetic flux passing through the persistent current loop 101 is quantized.

[0036] The accumulation of magnetic flux quanta can be seen as analogous to a phase particle crossing a potential hill in the washboard potential of the Josephson junction 102. The shunt resistive element 201 serves to damp the system after "kicking" the potential hill (with a pulse) so that the phase particle can stop at the next valley before crossing the next (undesirable) hill of the washboard potential.

[0037] The signal lines may be implemented, for example, as traces on a printed circuit board (PCB), traces on a silicon chip, cables, transmission lines, waveguides, etc. The signal lines may include superconducting signal lines.

[0038] Quantum computing units (QPUs) typically require fine-tuning each qubit and the couplers between qubits using high-fidelity direct current (DC) biasing during a calibration phase. Fine-tuning can, for example, compensate for manufacturing differences between qubits and / or couplers. The bias current can be provided, for example, by a programmable low-noise DC source. For example, for a 1000-qubit QPU, this would be about 2500 DC wires at room temperature and a corresponding number of low-drift DC sources. The cost and complexity of operating 2500 high-fidelity programmable DC sources per QPU could require significant infrastructure. Furthermore, if the QPU is in a cryostat, a large number of DC wires to the cryostat may also be required. A continuous current may also be required during operation of the QPU to maintain the fine-tuning.

[0039] The apparatus 100 can set the persistent current for each quantum computing element by providing an initial persistent current using an external current source. The apparatus 100 can be implemented, for example, on the QPU chip itself or as a stacked auxiliary chip that can operate at cryostat temperatures in a persistent state without power consumption due to the persistent current. Thus, the apparatus 100 may not contribute to the heat load of the cryostat either. The external current may be disconnected, and thus noise from room temperature sources may not affect the QPU. A single high-fidelity external DC source may be used in series to set the persistent current for any number of qubits and couplers.

[0040] Apparatus 100 may require two sets of sqrt(N) signal lines for N quantum computing elements. Thus, for a 2500 computing element chip, 50+50 lines may be required from room temperature. At room temperature, a simple switch matrix may be used to set all 2500 persistent currents using only one or two current sources.

[0041] Apparatus 100 can, for example, fine-tune the frequency of each qubit and coupler of the QPU during a calibration phase. Because of the persistent current in persistent current loop 101, continuous fine-tuning currents are not required during operation of the QPU.

[0042] If necessary due to the limitations of magnetic flux quantization, inductance can be added to the persistent current loop for additive effect using a Josephson junction, multiple Josephson junctions in series, or multiple parallel persistent current loops with various couplings. The Josephson inductance can be made relatively large compared to the geometric inductance. The maximum number of magnetic flux quanta that can be placed in a persistent current loop is proportional to the total loop inductance (for a given shunted Josephson junction critical current), and thus the larger the loop inductance, the more persistent current levels are available and therefore the easier it is to tune a wider range.

[0043] FIG. 2 shows a schematic diagram of an apparatus for frequency shifting of a quantum computing device according to another embodiment.

[0044] According to one embodiment, each persistent current loop 101 of the plurality of persistent current loops is electrically coupled to a corresponding signal line of the first plurality of signal lines 105 and a corresponding signal line of the second plurality of signal lines 106, and is configured to induce a persistent current in the persistent current loop, via at least one Josephson junction 102, in response to a current between the corresponding signal line of the first plurality of signal lines 105 and the corresponding signal line of the second plurality of signal lines 106 exceeding a critical current of the at least one Josephson junction 102.

[0045] In the embodiment of Fig. 2, each persistent current loop includes a Josephson junction 102 that is shunted using a shunt resistive element 201. The shunted Josephson junction 101 and at least one inductive element 103 form the persistent current loop 101. The shunt resistive element 201 serves to damp oscillations, and thus allows the persistent current loop to acquire a magnetic flux quantum in a controllable manner during biasing. Once a persistent current is established in the persistent current loop 101, the shunt resistive element 201 plays no role, i.e., in the steady state, there is no voltage across the shunt resistive element 201 and no current flows through it. Instead, the current flows only through the Josephson junction 101 and the at least one inductive element 103.

[0046] For example, a current may be generated by a pulse in a corresponding signal line of the first plurality of signal lines 105, and the current generated by the pulse may flow into a corresponding signal line of the second plurality of signal lines 106 via an addressed persistent current loop, or vice versa.

[0047] Since the signal line is coupled to the persistent current loop and its dynamics, neither the current nor the voltage is exactly constant during the pulse. A low impedance voltage source can provide a pulse to the signal line with some impedance, including real and imaginary components, which will cause a current to flow in the superconducting signal line and some response in the internal dynamics of the persistent current loop. The current in the superconducting signal line is set by the impedance of the feeder line, some of which is real. However, if the superconducting line is weakly coupled to the current loop, we can think of an almost constant current pulse whose value is set by other impedances in the system. The feeder line could possibly have some filtering and resistors in front of the superconducting line on the chip.

[0048] When the critical current of at least one Josephson junction 102 is exceeded, a magnetic flux quantum is added to the persistent current loop 101 .

[0049] The electrical coupling may include, for example, galvanic coupling, or any other type of coupling that allows current to flow between a corresponding signal line of the first plurality of signal lines 105 and a corresponding signal line of the second plurality of signal lines 106 through at least one Josephson junction 102.

[0050] Each persistent current loop can be addressed by driving a pulse to a corresponding signal line of the first plurality of signal lines 105, allowing current to flow through the addressed persistent current loop to a corresponding signal line of the second plurality of signal lines 106. Other signal lines of the first plurality of signal lines 105 and / or the second plurality of signal lines 106 may be floating. Thus, current can flow from a corresponding signal line of the first plurality of signal lines 105 through the persistent current loop to a corresponding signal line of the second plurality of signal lines 106. The current flow can generate a persistent current in the persistent current loop.

[0051] According to one embodiment, each persistent current loop 101 is electrically coupled to a corresponding signal line of the first plurality of signal lines 105 via at least one first coupling resistive element and / or at least one first coupling inductive element 202, and each persistent current loop 101 is coupled to a corresponding signal line of the second plurality of signal lines 106 via at least one second coupling resistive element and / or at least one second coupling inductive element 203.

[0052] The coupling inductive elements 202, 203 and / or the coupling resistive elements play a different role than the shunt resistive element 201. Whereas the shunt resistive element 201 damps the Josephson oscillation in that particular loop, the coupling inductive elements 202, 203 and / or the coupling resistive elements modify the circuit dynamic and favor a particular current path by allowing current to accumulate only in one persistent current loop instead of multiple persistent current loops. When using vertical-horizontal grid addressing without floating loops, there are several weak current paths that, without these elements, could accumulate persistent current in other loops as well. The coupling inductive elements 202, 203 and / or the coupling resistive elements ensure that the unwanted current remains below the accumulation threshold. In the resulting steady state, current is applied only to the addressed persistent current loop, even though there may be some current in other loops during the pulse.

[0053] The coupling resistive and / or inductive elements 202, 203 can limit the flow of reverse current to non-addressed persistent current loops and give priority to the addressed persistent current loops, preventing them from adding flux quanta to other loops. Without the coupling resistive and / or inductive elements 202, 203, some quanta may also end up in non-addressed persistent current loops. Furthermore, the coupling resistive elements may lead to a stabilization system.

[0054] For example, in the embodiment of FIG. 2, each persistent current loop 101 is electrically coupled to a corresponding signal line of the first plurality of signal lines 105 via a first coupling inductor element 202 and to a corresponding signal line of the second plurality of signal lines 106 via a second coupling inductor element 203.

[0055] In other embodiments, the first coupling inductor element 202 may be replaced by a first coupling resistive element, and the second coupling inductor element 203 may be replaced by a second coupling resistive element.

[0056] FIG. 3 shows a schematic diagram of an apparatus for frequency shifting of a quantum computing device according to another embodiment.

[0057] According to one embodiment, each persistent current loop 101 of the multiple persistent current loops is inductively coupled to a corresponding signal line of the first plurality of signal lines 105 and a corresponding signal line of the second plurality of signal lines 106, and is configured to induce a persistent current in the persistent current loop 101 in response to a first pulse in the corresponding signal line of the first plurality of signal lines 105 and a second pulse in the corresponding signal line of the second plurality of signal lines 106 when a total induced current due to the first pulse and the second pulse in the persistent current loop is greater than a critical current of at least one Josephson junction 102 of the persistent current loop 101.

[0058] 3, each persistent current loop includes a first inductive element 301 and a second inductive element 302, each signal line of the first plurality of signal lines 105 includes a third inductive element 303, and each signal line of the second plurality of signal lines 106 includes a fourth inductive element 304. The first inductive element 301 may be inductively coupled to the third inductive element 303, and the second inductive element 302 may be inductively coupled to the fourth inductive element 304. The first inductive element 301 and / or the second inductive element 304 may correspond to at least one inductive element 103.

[0059] 3, the persistent current loop includes a Josephson junction 102 and a shunt resistive element 201. This may also be referred to as a shunted RF superconducting quantum interference device (SQUID).

[0060] The additive effect of the first and second pulses on the persistent current loop 101 allows for arbitrary addition or subtraction of flux quanta in the addressed persistent current loop while leaving the quanta unchanged in the unaddressed persistent current loop. The amplitude of the single pulse can be set to a suitable value below the critical current of the Josephson junction 102, but such that the two pulses add up to a value above the critical current.

[0061] FIG. 4 shows a schematic diagram of a coupling between a persistent current loop and a quantum computing device according to one embodiment.

[0062] According to one embodiment, each persistent current loop 101 of the plurality of persistent current loops is inductively coupled to a corresponding quantum computing element 402 and configured to cause a shift in frequency of the corresponding quantum computing element 402 via a magnetic field induced by the persistent current.

[0063] 4, the persistent current loop 101 is electrically coupled to an inductive element 401. The inductive element 401 may correspond to at least one of the inductive elements 103. The inductive element 401 may be configured to cause a shift in frequency of a corresponding quantum computing element 402 via a magnetic field induced by a persistent current in the inductive element 401.

[0064] According to one embodiment, each quantum computing element 402 includes at least one Josephson junction 403 , and the magnetic field is configured to tune a Josephson inductance of the at least one Josephson junction 403 of the corresponding quantum computing element 402 .

[0065] For example, in the embodiment of Figure 4, quantum computing element 402 includes two Josephson junctions 403 forming a SQUID. A SQUID may include two Josephson junctions connected in a loop. Such a loop may be referred to as a SQUID loop. A SQUID may function, for example, as a qubit or as a coupler between qubits.

[0066] In some embodiments, the apparatus 100 can be implemented on a separate chip from the quantum computing device 402. The inductive device 401 can be implemented on the same chip as the quantum computing device 402, and each inductive device 401 can be electrically coupled to a persistent current loop 101 on the other chip.

[0067] Although some embodiments may be disclosed herein with reference to certain types of qubits, these qubit types are merely exemplary. In any embodiment disclosed herein, the qubits may be implemented in a variety of ways and using a variety of techniques.

[0068] As used herein, any qubit may include, for example, a flux qubit, a phase qubit, and / or a transmon qubit. Different types of qubits can be provided with Josephson inductance tunability with simple circuit modifications.

[0069] FIG. 5 shows a plotted representation of a simulation of the current in different persistent current loops according to one embodiment.

[0070] In the embodiment of Fig. 5, the curves represent the current in different persistent current loops in an apparatus 100 similar to that presented in the embodiment of Fig. 2. Curve 501 corresponds to the current in the persistent current loop of the target, while the other curves represent the current in the other persistent current loops.

[0071] In the simulations disclosed herein, the RCSJ model for Josephson junctions is used. The current realized in the superconducting signal line during the pulse is not shown since it is of little importance as long as the current in the persistent current loop behaves in the desired way. The simulations were performed considering the pulse source as 50Ω and the on-chip superconducting line as a pure weakly coupled inductance or a 0Ω wire depending on the case.

[0072] Initially, the external current and the persistent current are zero. All columns and rows are open. The external current is then pulsed through one persistent current loop from t=20ns to t=50ns while the other signal lines remain open. During this period, the persistent current accumulates one flux quantum at a time. After the pulse, the external current can be disconnected. A reverse pulse can be used to remove the quantum from the persistent current loop.

[0073] It should be understood that any parameter values, such as time scales, are merely exemplary and may vary based on the design of the device 100 .

[0074] FIG. 6 shows a plotted representation of a simulation of the current flowing through the Josephson junctions of each persistent current loop.

[0075] In the embodiment of Fig. 6, the curves represent the currents flowing in the Josephson junctions of different persistent current loops in a device 100 similar to that presented in the embodiment of Fig. 2. Curve 601 corresponds to the current in the Josephson junction of an addressed persistent current loop. Each oscillation corresponds to a quantum of magnetic flux applied to the addressed persistent current loop. After t=50 ns, a persistent current can be observed in curve 601.

[0076] FIG. 7 shows a plotted representation of a simulation of the current flowing through the resistive element of each persistent current loop.

[0077] In the embodiment of Fig. 7, the curves represent the current through the resistive element of the different persistent current loops in the device 100 similar to that presented in the embodiment of Fig. 2. Curve 701 corresponds to the current through the resistive element of the addressed persistent current loop. Each peak corresponds to a flux quantum applied to the addressed persistent current loop. After t=50ns, when no flux quantum is applied to the addressed persistent current loop, no current flows through the resistive element, as can be observed from curve 701.

[0078] FIG. 8 shows a plotted representation of a simulation of the current flowing in the persistent current loop for different pulse lengths.

[0079] In the embodiment of Fig. 8, the curves represent the current in different persistent current loops in an apparatus 100 similar to that presented in the embodiment of Fig. 3. The solid curves represent the current in addressed persistent current loops for different pulse lengths, and the dotted curves represent the current in non-addressed persistent current loops.

[0080] Initially, the current is zero. Then, a flux pulse is provided by an external source via one of the first plurality of signal lines 105 and one of the second plurality of signal lines 106, which crosses in the addressed persistent current loop. As can be seen in FIG. 8, the pulse length affects the number of persistent flux quanta that are added to the addressed persistent current loop. The persistent current can be observed in FIG. 8 as the current remaining in the steady state after the pulse. There is no persistent current in the persistent current loops that are not addressed.

[0081] FIG. 9 shows a plotted representation of a simulation of the current flowing through the resistive element of an addressed persistent current loop.

[0082] In the embodiment of Fig. 9, the curves represent the current in the resistive element of an addressed persistent current loop for different pulse lengths in a device 100 similar to that presented in the embodiment of Fig. 3. As can be seen from Fig. 9, power is consumed by the resistive element only during the transition before the persistent current loop reaches a steady state.

[0083] FIG. 10 shows a plotted representation of a simulation of the current flowing in the persistent current loops as the persistent current is applied and removed for one persistent current loop.

[0084] In the embodiment of Fig. 10, a persistent current is added to the addressed persistent current loop via a pulse from t = 20ns to t = 30ns. After the pulse, a persistent current can be observed as a negative persistent current between t = 30ns and t = 40ns in the addressed persistent current loop, but no persistent current is observed in the non-addressed persistent current loop. From t = 40ns to t = 45ns, a pulse of the opposite polarity is used to remove the persistent current from the addressed persistent current loop. As a result, a reduced persistent current can be observed after the pulse, but again, there is no persistent current in the non-addressed persistent current loop.

[0085] FIG. 11 shows a schematic diagram of a quantum computing system 1100 according to one embodiment.

[0086] According to one embodiment, the quantum computing system 1100 includes a plurality of qubits 1101 and an apparatus 100. At least one persistent current loop 101 of the plurality of persistent current loops of the apparatus 100 is coupled to a corresponding qubit of the plurality of qubits 1101.

[0087] In some embodiments, each persistent current loop 101 of the plurality of persistent current loops of the apparatus 100 may be coupled to a corresponding quantum bit of the plurality of quantum bits 1101 .

[0088] 11, three persistent current loops 101 are shown in the device 100. Each persistent current loop 101 shown is coupled to a corresponding quantum bit of the plurality of quantum bits 1101.

[0089] According to one embodiment, the quantum computing system 1100 further includes a plurality of couplers 1102, each coupled to two quantum bits of the plurality of quantum bits 1101 and configured to control the coupling between the two quantum bits, and at least one persistent current loop of the plurality of persistent current loops of the device 100 is coupled to a corresponding coupler of the plurality of couplers 1102.

[0090] In some embodiments, each persistent current loop of the plurality of persistent current loops of the apparatus 100 is coupled to a corresponding coupler of the plurality of couplers 1102 .

[0091] In other embodiments, the plurality of persistent current loops may include first and second subsets of persistent current loops, each persistent current loop in the first subset may be coupled to a corresponding qubit in the plurality of qubits 1101, and each persistent current loop in the second subset may be coupled to a corresponding coupler in the plurality of couplers 1102.

[0092] According to one embodiment, each qubit in the plurality of qubits 1101 includes at least one Josephson junction and / or each coupler in the plurality of couplers 1102 includes at least one Josephson junction.

[0093] According to one embodiment, the plurality of qubits 1101 includes superconducting qubits.

[0094] According to one embodiment, the quantum computing system further includes a control unit 1103 coupled to the first and second plurality of signal lines of the apparatus 100 and configured to shift the frequency of a target quantum bit of the plurality of quantum bits 1101 by providing a pulse to a signal line of the first plurality of signal lines corresponding to the target quantum bit and / or a signal line of the second plurality of signal lines corresponding to the target quantum bit.

[0095] According to another embodiment, control unit 1103 is configured to shift the frequency of a target quantum bit of the plurality of quantum bits 1101 by providing a pulse to a signal line of the first plurality of signal lines corresponding to the target quantum bit and allowing a current caused by the pulse to flow, via the persistent current loop, to a signal line of the second plurality of signal lines corresponding to the target quantum bit. This may be the case, for example, when apparatus 100 is implemented in a manner similar to the embodiment of FIG.

[0096] According to another embodiment, the control unit 1103 is configured to shift the frequency of a target quantum bit of the plurality of quantum bits 1101 by providing a first pulse to a signal line of the first plurality of signal lines corresponding to the target quantum bit and providing a second pulse to a signal line of the second plurality of signal lines corresponding to the target quantum bit, wherein a total induced current due to the first pulse and the second pulse in the target persistent current loop is greater than a critical current of at least one Josephson junction of the target persistent current loop. This may be the case, for example, when the apparatus 100 is implemented in a manner similar to the embodiment of FIG.

[0097] When system 1100 is operating, device 100 and / or plurality of qubits 1101 may be physically located, such as in a cryostat. The cryostat may cool device 100 and / or plurality of qubits 1101 to cryogenic temperatures. This may be necessary when a qubit in the plurality of qubits is, for example, a superconducting qubit. Control unit 1103 may be located outside of the cryostat.

[0098] In the embodiment of FIG. 11, the connection between the device 100 and the control unit 1103 is shown diagrammatically as a single connection, however, the control unit 1103 may be electrically coupled to each signal line of the first plurality of signal lines and the second plurality of signal lines.

[0099] FIG. 12 shows a schematic diagram of a control unit according to one embodiment.

[0100] The control unit 1103 may include at least one processor 1201. The at least one processor 1201 may include one or more of a variety of other processing devices including, for example, a coprocessor, a microprocessor, the control unit 1103, a digital signal processor (DSP), processing circuitry with or without a DSP, or integrated circuits such as, for example, an application specific integrated circuit (ASIC), a field programmable gate array (FPGA), a microprocessor unit (MCU), a hardware accelerator, a dedicated computer chip, or the like.

[0101] The control unit 1103 may further include a memory 1202. The memory 1202 may be configured to store, for example, a computer program, etc. The memory 1202 may include one or more volatile memory devices, one or more non-volatile memory devices, and / or a combination of one or more volatile and non-volatile memory devices. For example, the memory 1202 may be embodied as a magnetic storage device (such as a hard disk drive, a floppy disk, a magnetic tape, etc.), a magneto-optical storage device, and a semiconductor memory (such as a mask ROM, a PROM (programmable ROM), an EPROM (erasable PROM), a flash ROM, a RAM (random access memory), etc.).

[0102] The control unit 1103 may further include other components not shown in the embodiment of Fig. 12. The control unit 1103 may, for example, include an input / output bus for connecting the control unit 1103 to the device 100. Furthermore, a user can control the control unit 1103 via the input / output bus. The control unit 1103 may further include a means for supplying the first / second pulse to the signal line. For example, the control unit 1103 may include a DC source, such as a direct current source.

[0103] When the control unit 1103 is configured to implement a function, several components of the control unit 1103, such as, for example, the at least one processor 1201 and / or the memory 1202, may be configured to implement the function. Furthermore, when the at least one processor 1201 is configured to implement a function, the function may be implemented using program code included in, for example, the memory 1202.

[0104] The control unit 1103 may be implemented using, for example, a computer, other computing device, or the like.

[0105] Any ranges or device values ​​described herein may be expanded or modified without losing the effect sought, and any embodiment may be combined with another embodiment unless expressly prohibited.

[0106] Although the subject matter has been described in language specific to structural features and / or acts, it should be understood that the subject matter defined in the appended claims is not necessarily limited to the specific features or acts described above. Rather, the specific features and acts described above are disclosed as example ways of implementing the claims, and other equivalent features and acts are intended to be within the scope of the claims.

[0107] It will be understood that the benefits and advantages described above may relate to one embodiment or to several embodiments. The embodiments are not limited to those that solve any or all of the problems described or those that have any or all of the benefits and advantages described. Further, it will be understood that references to "an" or "an" item may refer to one or more of those items.

[0108] The steps of the methods described herein may be performed in any suitable order, or simultaneously where appropriate. Additionally, individual blocks may be deleted from any method without departing from the spirit and scope of the subject matter described herein. Aspects of any of the embodiments described above may be combined with aspects of any other embodiment described to form further embodiments without losing the desired effect.

[0109] As used herein, the term "comprising" is used to mean inclusive of specified methods, blocks, or elements, but that such blocks or elements are not inclusive of an exclusive list and that a method or apparatus may include additional blocks or elements.

[0110] It will be understood that the above description is given by way of example only, and that various modifications may be made by those skilled in the art. The above specification, examples, and data provide a complete description of the structure and use of the exemplary embodiments. Although various embodiments have been described above with a certain degree of particularity, or with reference to one or more individual embodiments, those skilled in the art may make many modifications to the disclosed embodiments without departing from the spirit or scope of the present specification. [Explanation of symbols]

[0111] 100 devices 102 Josephson Junction 103 Inductive elements 105 first plurality of signal lines 106 second plurality of signal lines 201 Shunt resistor element 202 First coupling inductor element 203 Second coupling inductor 301 First inductive element 302 Second inductive element 303 Third Inductive Element 304 Fourth Inductive Element 401 Inductive element 402 Quantum Computing Device 403 Josephson Junction 1100 Quantum Computing System 1101 qubit 1102 Coupler 1103 Control Unit 1201 Processor 1202 Memory

Claims

1. An apparatus (100) for frequency shifting of a quantum computing device, comprising: a plurality of persistent current loops (101), each of which includes at least one Josephson junction (102), at least one shunt resistive element (201), and at least one inductive element (103), each of which is capable of being coupled to a corresponding quantum computing element (402); a first plurality of signal lines (105), each of the persistent current loops (101) being coupled (110) to a corresponding one of the first plurality of signal lines (105); a second plurality of signal lines (106), each persistent current loop (101) of the plurality of persistent current loops being coupled (111) to a corresponding signal line of the second plurality of signal lines (106); each persistent current loop (101) of the plurality of persistent current loops is configured to induce a persistent current in the persistent current loop in response to a pulse on a corresponding signal line of the first plurality of signal lines (105) and / or a corresponding signal line of the second plurality of signal lines (106), the persistent current being configured to cause a shift in frequency of the corresponding quantum computing element (402); Equipment (100).

2. 2. The apparatus of claim 1, wherein each persistent current loop (101) of the plurality of persistent current loops is electrically coupled to a corresponding signal line of the first plurality of signal lines (105) and a corresponding signal line of the second plurality of signal lines (106) and is configured to induce the persistent current in the persistent current loop (101) via the at least one Josephson junction (102) in response to a current between the corresponding signal line of the first plurality of signal lines (105) and the corresponding signal line of the second plurality of signal lines (106) exceeding a critical current of the at least one Josephson junction (102).

3. 3. The apparatus (100) of claim 2, wherein each persistent current loop (101) is electrically coupled to the corresponding signal line of the first plurality of signal lines (105) via at least one first coupling resistive element and / or at least one first coupling inductive element (202), and each persistent current loop (101) is coupled to the corresponding signal line of the second plurality of signal lines (106) via at least one second coupling resistive element and / or at least one second coupling inductive element (203).

4. 2. The apparatus of claim 1, wherein each persistent current loop (101) of the plurality of persistent current loops is inductively coupled to the corresponding signal line of the first plurality of signal lines (105) and the corresponding signal line of the second plurality of signal lines (106) and is configured to induce the persistent current in the persistent current loop (101) in response to the first pulse in the corresponding signal line of the first plurality of signal lines (105) and the second pulse in the corresponding signal line of the second plurality of signal lines (106) when a total induced current due to a first pulse and a second pulse in the persistent current loop is greater than a critical current of the at least one Josephson junction (102) of the persistent current loop (101).

5. 5. The apparatus of claim 1, wherein each persistent current loop of the plurality of persistent current loops is inductively coupled to a corresponding quantum computing element and configured to cause the shift in the frequency of the corresponding quantum computing element via a magnetic field induced by the persistent current.

6. 6. The apparatus (100) of claim 5, wherein each quantum computing element (402) includes at least one Josephson junction (403), and the magnetic field is configured to adjust a Josephson inductance of the at least one Josephson junction (403) of the corresponding quantum computing element (402).

7. The apparatus (100) of any one of claims 1 to 6, wherein each quantum computing element (402) comprises a qubit or a coupler between qubits.

8. A quantum computing system (1100) comprising a plurality of quantum bits (1101) and an apparatus (100) according to any one of claims 1 to 7, wherein at least one persistent current loop (101) of the plurality of persistent current loops of the apparatus (100) is coupled to a corresponding quantum bit of the plurality of quantum bits (1101).

9. 9. The quantum computing system (1100) of claim 8, further comprising a plurality of couplers (1102), each coupler coupled to two quantum bits of the plurality of quantum bits (1101) and configured to control coupling between the two quantum bits, and at least one persistent current loop of the plurality of persistent current loops of the device (100) is coupled to a corresponding coupler of the plurality of couplers (1102).

10. 10. The quantum computing system (1100) of claim 8 or claim 9, wherein each quantum bit of the plurality of quantum bits includes at least one Josephson junction and / or each coupler of the plurality of couplers includes at least one Josephson junction.

11. 11. The quantum computing system (1100) of claim 8, wherein the plurality of qubits comprises a superconducting qubit.

12. 12. The quantum computing system (1100) of claim 8, further comprising a control unit (1103) coupled to the first and second plurality of signal lines of the device (100) and configured to shift the frequency of a target quantum bit of the plurality of quantum bits (1101) by supplying a pulse to one signal line of the first plurality of signal lines corresponding to a target quantum bit and / or one signal line of the second plurality of signal lines corresponding to the target quantum bit.

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