Equipment for quantum computing

Abstract

According to one embodiment, an apparatus for quantum computing comprises a plurality of quantum computing units, each quantum computing unit comprising a plurality of qubits arranged to perform a quantum computation according to a plurality of control signals and to provide at least one output signal according to a result of the quantum computation; a control unit for providing the plurality of control signals; a signal distribution device for transmitting the plurality of control signals to the plurality of quantum computing units, the signal distribution device configured to distribute each control signal to each quantum computing unit, the control unit configured to cause each quantum computing unit to perform a separate instance of a quantum computation; and a readout unit configured to obtain at least one output signal from each quantum computing unit and to perform at least one statistical operation based on the output signals, thereby obtaining an overall quantum computing result.

Description

[Technical field]

[0001] The present disclosure relates to quantum computing, and more particularly to apparatus for quantum computing and quantum computing systems. [Background technology]

[0002] It has been predicted that quantum computing will achieve exponential speedups in certain tasks compared to classical computing. However, results from quantum computing may be non-deterministic due to non-idealities in quantum computing units or due to the principles of certain methodologies used in quantum computing. Therefore, quantum computations typically need to be performed multiple times to obtain meaningful results. This significantly increases the total execution time of quantum computations, which may hinder the overall performance of quantum computing and limit the range of applications. While a single quantum processor may have a large number of qubits, the complexity of wiring copies of high-quality quantum processors as well as issues in calibration and fabrication have typically limited the number of quantum processors inside to one or at most a small number to be set up. 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] The object is to provide an apparatus for quantum computing and a quantum computing system. The above 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 aspect, an apparatus for quantum computing includes a plurality of quantum computing units, each of which includes a plurality of qubits arranged to perform a quantum computation according to a plurality of control signals provided to the quantum computing units and to provide at least one output signal according to a result of the quantum computation; a control unit for providing a plurality of control signals to the plurality of quantum computing units; a signal distribution device for transmitting a plurality of control signals generated from the control unit to the plurality of quantum computing units, the signal distribution device being configured to distribute each control signal in the plurality of control signals generated from the control unit to each quantum computing unit in the plurality of quantum computing units, the control unit being configured to cause each quantum computing unit in the plurality of quantum computing units to perform a separate instance of a quantum computation via the plurality of control signals and the signal distribution device; and a readout unit configured to obtain at least one output signal from each quantum computing unit in the plurality of quantum computing units, and perform at least one statistical operation based on the output signal, thereby obtaining an overall quantum computation result. The apparatus can, for example, obtain a result for the quantum computation faster.

[0006] In one implementation of the first aspect, each quantum computing unit in the plurality of quantum computing units corresponds to a quantum processing unit QPU, a core in a multi-core QPU, or a subunit of a QPU. The apparatus can be implemented, for example, with various levels of integration.

[0007] In another implementation of the first aspect, the signal distribution device is configured to distribute each control signal in the plurality of control signals generated by the control unit to each quantum computing unit in the plurality of quantum computing units using at least one T-junction, at least one power splitter, at least one Wilkinson power splitter, at least one directional coupler, and / or at least one hybrid coupler. The device can, for example, efficiently distribute radio frequency control signals to the plurality of quantum computing units.

[0008] In another implementation of the first aspect, the apparatus further comprises a tuning device configured to adjust at least one characteristic of the plurality of control signals distributed by the signal distribution device, the at least one characteristic including at least one of frequency, amplitude, phase, and / or relative timing. The apparatus can, for example, fine-tune the control signals according to the characteristics of each quantum computing unit.

[0009] In another implementation of the first aspect, the tuning device further comprises at least one voltage-controlled attenuator configured to adjust at least one control signal in the plurality of control signals distributed by the signal distribution device, the device being capable of, for example, efficiently fine-tuning a radio frequency control signal.

[0010] In another implementation of the first aspect, the at least one voltage controlled attenuator comprises at least one high electron mobility transistor, at least one tunable reactive impedance element, at least one superconducting quantum interference device, and / or at least one varactor diode. The apparatus can, for example, efficiently fine tune a radio frequency control signal.

[0011] In another implementation of the first aspect, the output signals from the multiple quantum computing units are time-multiplexed, and the readout unit is further configured to obtain an output signal from each quantum computing unit in the multiple quantum computing units according to the time-multiplexing. The apparatus can, for example, transmit the output signals from the quantum computing units to the readout unit with a reduced number of signal lines.

[0012] In another implementation of the first aspect, the apparatus further comprises a delay line coupled to the multiple quantum computing units and configured to time multiplex output signals from the multiple quantum computing units. The apparatus can, for example, efficiently time multiplex the output signals via the delay line.

[0013] In another implementation of the first aspect, the readout unit further comprises a summing device, and the readout unit is configured to perform at least one statistical operation based on the output signals by coherently adding the output signals via the summing device. The device can, for example, efficiently perform the at least one statistical operation via the coherent adding.

[0014] In another implementation of the first aspect, each quantum computing unit in the plurality of quantum computing units further comprises a plurality of frequency tuning elements configured to tune a qubit frequency of the plurality of qubits according to the frequency tuning signal. The apparatus can, for example, fine-tune the qubit frequency.

[0015] In another implementation of the first aspect, each quantum computing unit in the plurality of quantum computing units further comprises a plurality of capacitance tuning elements configured to tune a capacitance of the plurality of qubits according to a capacitance tuning signal. The apparatus can, for example, fine-tune the qubit capacitance.

[0016] In another implementation of the first aspect, the plurality of qubits comprises superconducting qubits.

[0017] In another implementation of the first aspect, the at least one statistical operation includes at least one of a mean, a variance, and / or a cross-entropy.

[0018] In another implementation of the first aspect, the apparatus further comprises a cryostat, and the multiple quantum computing units and the signal distribution device are disposed inside the cryostat. The apparatus can, for example, reduce the number of signal lines that need to be extended within the cryostat.

[0019] According to a second aspect, a quantum computing system comprises a plurality of devices according to the first aspect.

[0020] 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 connection with the accompanying drawings.

[0021] In the following, example embodiments are described in more detail with reference to the accompanying figures and drawings. [Brief description of the drawings]

[0022] [Figure 1] FIG. 1 is a schematic diagram of an apparatus for quantum computing according to one embodiment. [Diagram 2] 1 is a schematic diagram of an apparatus for quantum computing further comprising a tuning device according to an embodiment; [Diagram 3] 1 is a schematic diagram of an apparatus for quantum computing further comprising a delay line according to an embodiment; [Figure 4] FIG. 2 is a schematic diagram of a qubit and a frequency tuning element according to one embodiment. [Diagram 5] FIG. 2 is a schematic diagram of a control unit according to one embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0023] In the following, like reference numerals are used to denote like parts in the accompanying drawings.

[0024] In the following description, reference is made to the accompanying drawings which form a part of this disclosure and which illustrate, by way of example, specific aspects in which the disclosure may be implemented. It is understood that other aspects may be utilized and structural or logical changes may be made without departing from the scope of the disclosure. The following detailed description is therefore not to be taken in a limiting sense, nor is it the appended claims which define the scope of the disclosure.

[0025] For example, it is 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 particular method steps are described, a corresponding device may include units performing the described method steps, even if such units are not explicitly described or illustrated in the figures. On the other hand, for example, where a particular apparatus is described based on functional units, a corresponding method may include steps performing the described functions, even if such steps are not explicitly described or illustrated in the figures. Furthermore, it is understood that features of various example aspects described herein may be combined with each other, unless otherwise specified.

[0026] FIG. 1 illustrates a schematic diagram of an apparatus for quantum computing according to one embodiment.

[0027] According to one embodiment, apparatus 100 comprises a plurality of quantum computing units 101, each quantum computing unit comprising a plurality of qubits arranged to perform a quantum computation according to a plurality of control signals provided to the quantum computing unit, and to provide at least one output signal according to a result of the quantum computation.

[0028] The plurality of qubits may comprise superconducting qubits, such as, for example, transmon qubits, flux qubits, charge qubits, phase qubits, or fluxonium qubits.

[0029] 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.

[0030] Each control signal in the plurality of control signals can control, for example, coupling between qubits, initialization of the qubits, the state of the qubits, and / or any other characteristic of the qubits required to perform a quantum computation.

[0031] The control signal may consist of, for example, a radio frequency (RF) signal or an optical signal depending on the implementation of the multiple quantum computing units 101.

[0032] The output signal may also be referred to as a read signal or the like.

[0033] The control signal may also be referred to as a control voltage, a control pulse, etc.

[0034] The apparatus 100 may further comprise a control unit 102 for providing a plurality of control signals 104 to the plurality of quantum computing units 101 .

[0035] 1 illustrates only one signal line originating from control unit 102, this is merely for clarity of illustration. There may be any number of signal lines originating from control unit 102. For example, if N control signals are needed for each quantum computing unit in multiple quantum computing units 101, then multiple control signals 104 may consist of N control signals, and for each control signal there may be a corresponding signal line originating from control unit 102.

[0036] The apparatus 100 may further comprise a signal distribution device 103 for transmitting a plurality of control signals 104 originating from the control unit 102 to the plurality of quantum computing units 101. The signal distribution device 103 may be configured to distribute each control signal in the plurality of control signals 104 originating from the control unit 102 to each quantum computing unit in the plurality of quantum computing units 101.

[0037] For example, if N control signals are required for each quantum computing unit, then plurality of control signals 104 may include N control signals. Signal distribution device 103 may distribute each of the N control signals to each quantum computing unit in plurality of quantum computing units 101 such that N control signals are provided to each quantum computing unit. Thus, if there are M quantum computing units in plurality of quantum computing units 101, signal distribution device 103 may be configured to output N×M control signals.

[0038] The signal distribution device 103 may also be referred to as a fan-out device, a signal distribution device, a distributor, a one-to-multiple device, or the like.

[0039] The control unit 102 may be configured, via a plurality of control signals 104 and a signal distribution device 103, to cause each quantum computing unit in the plurality of quantum computing units 101 to perform a separate instance of a quantum computation.

[0040] Each quantum computing unit in the plurality of quantum computing units 101 may be nominally similar, such that each quantum computing unit may perform a quantum computation in a similar manner.

[0041] Signal distribution device 103 can distribute each control signal in multiple control signals 104 to each quantum computing unit in multiple quantum computing units 101 so that each quantum computing unit can perform a separate instance of a quantum computation. However, the results of a quantum computation may be non-deterministic, for example, due to non-idealities in the quantum computing units or due to the principles of certain quantum computing methods, and therefore each quantum computing unit may not produce the same results for the quantum computation.

[0042] An instance of a quantum computation may refer to a separate execution of a quantum computation. Each instance may perform a quantum computation separately from other instances. Each instance of a quantum computation may not produce the same results due to the non-deterministic nature of quantum computing.

[0043] Each quantum computing unit in the plurality of quantum computing units 101 may be a separate unit in the sense that there is no quantum coherence shared across the plurality of quantum computing units 101. As such, each quantum computing unit can perform quantum computations independently from each other.

[0044] Quantum computing can also be referred to as a quantum algorithm, a quantum circuit, and the like.

[0045] The apparatus 100 may further include a readout unit 105 configured to obtain at least one output signal 106 from each quantum computing unit in the plurality of quantum computing units 101 and perform at least one statistical operation based on the output signals 106, thereby obtaining an overall quantum computing result.

[0046] Because the quantum computing result may be non-deterministic at each quantum computing unit in the multiple quantum computing units 101, the readout unit 105 may need to perform statistical operations on the results to obtain an overall quantum computing result.

[0047] The overall quantum computing result may refer to a computation result obtained based on the results of each instance of quantum computing. For example, the overall quantum computing result may correspond to an average over the results of the different instances.

[0048] According to one embodiment, the at least one statistical operation includes at least one of a mean, a variance and / or a cross-entropy.

[0049] According to one embodiment, the signal distribution device 103 is configured to distribute each control signal in the plurality of control signals 104 generated from the control unit 102 to each quantum computing unit in the plurality of quantum computing units 101 using at least one T-junction, at least one power splitter, at least one Wilkinson power splitter, at least one directional coupler and / or at least one hybrid coupler.

[0050] The components disclosed above for distributing each control signal in the plurality of control signals 104 are merely exemplary. Alternatively, the signal distributor 103 may be configured to distribute each control signal in the plurality of control signals 104 originating from the control unit 102 to each quantum computing unit in the plurality of quantum computing units 101 using any other type of one or more signal distributors.

[0051] The apparatus 100 can speed up quantum computations, for example, through running multiple quantum computing units 101 substantially simultaneously, instead of repeating the same quantum computation many times on a single quantum computing unit. The apparatus 100 can run many similar (ideally identical) quantum computing units, for example, across quantum computing units, and perform the collection of statistics, rather than across time. For example, to achieve an accuracy of 1e-3, one million samples are required. Instead of running the same quantum computation on one quantum computing unit for 17 minutes, the same averaging can be done in one millisecond one shot on one million quantum computing units. This can be beneficial, for example, for variational quantum algorithms, where a computation may need to be repeated thousands or more times with different parameters. The apparatus 100 can enable feasible execution times for such algorithms, for example, given the integration of high performance computing, as well as exchanging data between classical and quantum computing steps. Another example is high frequency trading in financial applications, where a fraction of a second of wall clock time may be available for decision making. Quantum computing algorithms can be powerful in analyzing financial data, but previously they could not be used for this purpose because the iterations of the algorithms took too much time.

[0052] Multiple quantum computing units 101 can be placed in one or multiple dilution refrigerators. Multiple quantum computing units 101 can be provided with similar control signals and their outputs can be read out separately by readout unit 105 and post-processed, such as averaging.

[0053] In some embodiments, the signal distribution device 103 may be located in one or more dilution refrigerators, which may also be referred to as cryostats.

[0054] To overcome the large number of control signal lines required to operate multiple quantum computing units, device 100 includes a fan-out device 103, through which multiple control signals 104 can be distributed to each quantum computing unit in the multiple quantum computing units 101.

[0055] The control signal 104 can be an electromagnetic signal, such as a high frequency, such as multiple gigahertz or terahertz, an RF signal, or an optical signal. The generation of such a signal can be a technically complex task. The signal distribution device 103 can reduce the need for multiple high frequency signal sources, signal lines and / or other electronic components, thus reducing the technical complexity of the device 100.

[0056] The signal distribution device 103 may comprise a distributor capable of distributing a single input signal to multiple paths that address qubits in different quantum computing units in the multiple quantum computing units 101. The signal distribution may be done in a variety of ways. Different implementations may have different signal integrity, cross-coupling properties, losses, physical sizes and accessible frequency bands.

[0057] For example, the splitter can consist of a T-piece providing a 1:2 split of the RF signal, or a more general splitter providing a 1:N split. The ports of the splitter can be unmatched. A further generalization of the 1:2 splitter is the Wilkinson power splitter, which is matched at all ports with additional microwave loss mechanisms. The splitting can also be done with directional couplers such as 3 dB hybrids. Generalizations and / or combinations of the above examples are also practical, besides cascading many splitter stages to generate more outputs.

[0058] The signal distribution device 103 may further comprise impedance matching circuits, filters, isolators, attenuators or any other signal conditioning elements to improve the matching, noise rejection, and / or isolation of the different ports.

[0059] In an embodiment in which the quantum computing units 101 are based on neutral atomic qubits, such as, for example, nitrogen-vacancy (NV) center qubits, ion-trap qubits, and / or Rydberg atoms, the control signal 104 can consist of coherent light from a laser and the signal distribution device 103 can comprise, for example, one or more beam splitters. The lasers can be in different wavelength ranges for the techniques mentioned above.

[0060] According to one embodiment, each quantum computing unit in the plurality of quantum computing units 101 corresponds to a quantum processing unit (QPU), a core in a multi-core QPU, or a subunit of a QPU.

[0061] According to one embodiment, the apparatus 100 further comprises a cryostat, and the multiple quantum computing units 101 and the signal distribution device 103 are disposed inside the cryostat. Therefore, the number of signal lines that need to be extended inside the cryostat can be reduced since the signal distribution device 103 can distribute signals inside the cryostat. The control unit 102 can be disposed outside the cryostat.

[0062] The features disclosed herein can be implemented at a variety of different integration levels. For example, different QPU cores can be on the same chip, or the QPU cores can be on different chips in a single package. The package can be based on connecting the chips by wire bonding, or there can be a flip-chip solution where one or more carrier chips connect to one or more QPU cores. The carrier chip can include all or some of the microwave engineering solutions disclosed herein. Instead of a carrier chip, a printed circuit board (PCB) can carry the chips.

[0063] FIG. 2 illustrates a schematic diagram of an apparatus 100 for quantum computing further comprising a tuning device 201 according to one embodiment.

[0064] For example, manufacturing-related differences in the quantum computing units 101 may necessitate fine-tuning of the control signals after the signal distribution device 103.

[0065] According to one embodiment, the apparatus 100 further comprises a tuning device 201 configured to adjust at least one characteristic of the plurality of control signals distributed by the signal distribution device 103. The at least one characteristic may include at least one of frequency, amplitude, phase and / or relative timing.

[0066] For example, in the embodiment of Figure 2, the tuning device 201 comprises a tuning unit 202 and a number of tuning elements 203 coupled to the tuning unit 202. Only a single tuning element 203 is depicted for each quantum computing unit in the embodiment of Figure 2. However, there may be, for example, a separate tuning element 203 for each control signal output by the signal distribution device 103.

[0067] In some embodiments, the tuning unit 202 and the control unit 102 may be implemented by a single device. In some other embodiments, there may be a tuning unit 202 for each quantum computing unit in the plurality of quantum computing units 101.

[0068] According to one embodiment, the tuning device 201 further comprises at least one voltage controlled attenuator configured to adjust at least one control signal in the plurality of control signals distributed by the signal distribution device 103 .

[0069] According to an embodiment, the at least one voltage controlled attenuator comprises at least one high electron mobility transistor, at least one tunable reactive impedance element, at least one superconducting quantum interference device and / or at least one varactor diode.

[0070] The tuning device 201 may comprise, for example, a voltage-controlled attenuator capable of adjusting the amplitude of the control signal. The voltage-controlled attenuator may be implemented, for example, via a high electron mobility transistor (HEMT) used as a voltage-controlled resistor possibly supplemented by a passive resistor. Alternatively, the attenuator may comprise a tunable reactive impedance element implemented via a superconducting quantum interference device (SQUID) or a SQUID array or circuit based on varactor diodes. In some embodiments, precise phase control may be required and therefore phase shifters based on the above-mentioned reactive elements may also be used.

[0071] In some embodiments, the device 100 may further comprise a second tuning device for the output signal 106. Any disclosure herein regarding the tuning device 201 may also apply to the second tuning device.

[0072] FIG. 3 illustrates a schematic diagram of an apparatus for quantum computing 100 further comprising a delay line 301 according to one embodiment.

[0073] According to one embodiment, the output signals 106 from the multiple quantum computing units 101 are time multiplexed, and the readout unit 105 is further configured to obtain an output signal from each quantum computing unit in the multiple quantum computing units 101 according to the time multiplexing.

[0074] According to one embodiment, the apparatus 100 further comprises a delay line 301 coupled to the multiple quantum computing units 101 and configured to time multiplex the output signals 106 from the multiple quantum computing units.

[0075] Qubit readout can be arranged, for example, by time-multiplexing, i.e., separating in time, the output signals / pulses using delay lines. The physical length of each delay line can be controlled, for example, using high-inductance metamaterials, such as those based on Josephson junctions, or transduction into acoustic waves. The delay lines 301 can also be made tunable, for example, by using flux-controlled Josephson metamaterials.

[0076] FIG. 4 illustrates a schematic diagram of a qubit and frequency tuning element according to one embodiment.

[0077] Small fabrication tolerances among qubits and other quantum computing unit elements in multiple quantum computing units 101, as well as changing environmental conditions, may require in situ tuning.

[0078] According to one embodiment, each quantum computing unit in the plurality of quantum computing units 101 further comprises a plurality of frequency tuning elements configured to tune qubit frequencies of the plurality of qubits according to a frequency tuning signal.

[0079] For example, each qubit in the plurality of qubits may be coupled to a corresponding frequency tuning element. For superconducting qubits implemented using superconducting quantum interference devices (SQUIDs), this can be done by flux-controlling the Josephson coupling energy, and therefore the qubit frequency, with a DC or radio frequency signal.

[0080] Each qubit may have a basis state |g〉. As used herein, a basis state may refer to the quantum state of a qubit that has the lowest energy.

[0081] Each qubit may further have at least one excited state. The at least one excited state may include a lowest excited state |e〉. As used herein, the lowest excited state may refer to the quantum state of the qubit that is the second lowest in energy.

[0082] The ground state and lowest excited state of a qubit may correspond to a computational basis for the qubit. For example, the ground state |g〉 may correspond to the |0〉 state of the qubit and the lowest excited state |e〉 may correspond to the |1〉 state of the qubit, or vice versa. Other quantum states of the qubit may be referred to as non-computational states.

[0083] The energy gap between the ground state and the lowest excited state may correspond to the resonant frequency of the qubit. The energy gap may also be referred to as the qubit energy, and the corresponding frequency may also be referred to as the qubit frequency.

[0084] 4, qubit 405 comprises a SQUID 401 and a capacitive circuit 404. For SQUID 401 there is a corresponding frequency tuning element 402. Frequency tuning element 402 is electrically coupled to signal line 403. A frequency tuning signal may be provided via signal line 403. By providing a frequency tuning signal to signal line 403, the qubit frequency of qubit 405 may be adjusted. This may be referred to as flux tuning, where a magnetic flux generated by frequency tuning element 402 shifts the qubit frequency of the corresponding qubit 405.

[0085] In other embodiments, more than one qubit can be implemented by combining a SQUID 401 and a capacitive circuit 404 in a similar manner as in the embodiment of FIG. 4. For each qubit 405, there may be a corresponding frequency tuning element 402, for example consisting of a resonator. The resonator may be electrically coupled to a signal line 403. A frequency tuning signal may be provided via the signal line 403. By providing a signal with a frequency corresponding to the resonator's resonant frequency, the qubit frequency of the corresponding qubit 405 may be adjusted. Since each resonator may have a different resonant frequency, each resonator may be addressed using the same signal line 403 by appropriately choosing the frequency of the addressing signal.

[0086] The embodiments disclosed herein are only examples of frequency tuning of qubits, and frequency tuning can be implemented in a variety of other ways. For example, each qubit can include a SQUID tuning loop, and the frequency tuning signal comprises a direct current (DC) signal configured to vary a DC magnetic flux through the SQUID tuning loop.

[0087] According to one embodiment, each quantum computing unit in the plurality of quantum computing units 101 further comprises a plurality of capacitive tuning elements configured to tune the capacitance of the plurality of qubits according to a capacitive tuning signal.

[0088] For example, each qubit in the plurality of qubits may be coupled to a corresponding capacitive tuning element. Each capacitive tuning element may be configured to tune the capacitance of the corresponding qubit in response to a corresponding capacitive tuning signal. The capacitive tuning signal may be provided, for example, by the control unit 102 or by any other device / unit / module.

[0089] The capacitive tuning elements can compensate for small variations in the charging energy of the qubits, which can affect the spectrum of the qubit's non-computational states and thereby entangle the fidelity of the two-qubit gate operation. Each capacitive tuning element can consist of, for example, a metal plate affixed to a piezoelectric actuator.

[0090] For example, a transmon qubit can comprise two metallic (superconducting) electrodes connected with a Josephson junction. The qubit capacitance is then the electrical capacitance between the two electrodes and is determined by the geometry of the electrodes and the nearby dielectric. If the geometry is deformed, the qubit capacitance will change. The deformation of the geometry can be implemented, for example, using a third movable metallic electrode. The third metallic electrode can be moved, for example, using a piezoelectric element controlled by a capacitance tuning signal.

[0091] According to one embodiment, the readout unit 105 further comprises a summing device, and the readout unit 105 is configured to perform at least one statistical operation on the output signals 106 by coherently summing the output signals 106 via the summing device.

[0092] For example, the summing device may comprise at least one summing element. The output signals 106 may be summed using the at least one summing element. The implementation of the at least one summing element may depend on the implementation of the multiple quantum computing units 101. For example, if the multiple quantum computing units 101 comprise superconducting qubits, the output signals 106 may comprise RF signals. In such a case, the at least one summing element may comprise, for example, one or more RF combiners. If the multiple quantum computing units 101 comprise NV qubits, ion trap qubits, or neutral atom qubits, the output signals 106 are optical signals. In such a case, the at least one summing element may comprise any component capable of summing optical signals, such as one or more optical couplers, optical combiners, etc.

[0093] In some embodiments, the output signals are coherently summed before amplification. The benefit of this may be that only one amplifier chain is needed after summation. Alternatively, the output signals may be coherently summed after amplification. The summation of the output signals may correspond to taking an average of the output signals.

[0094] Each quantum computing unit in the plurality of quantum computing units 101 may include one or more output lines. Each output line may provide a corresponding output signal. Each output line may enable reading out the state of each qubit in the subset of qubits using frequency multiplexing.

[0095] Each output line can include a readout chain, which can include, for example, an amplification chain, a digital signal processor (DSP), and a discriminator that assigns a binary outcome ("0" or "1") to each qubit measurement.

[0096] If the statistics are an average of each individual qubit readout, then the statistics can be done at any point in the readout chain by counting the proportion of "1" measurements.

[0097] In embodiments requiring only an overall average single-qubit readout result, the output signals 106 from each quantum computing unit can be coherently summed prior to the amplification chain. This can be implemented, for example, by coupling the readout resonators of all quantum computing units to the same microwave feed line and correcting amplitude and phase misalignments between the quantum computing units with the tunable elements described above.

[0098] Alternatively, the expectation of any function of the measured bit string can be evaluated. The measured bit string can include a binary result for each qubit in the quantum computing unit. In this case, a separate readout chain may be required for each readout line of each quantum computing unit. Each execution instance of a quantum computation results in a new bit string. The collection of bit strings can be used as the output of a sampling problem. From the bit string samples, for example, the cross-entropy can be calculated. The cross-entropy can be used, for example, for cross-entropy benchmarking (XEB), where each experimentally observed bit string can be compared to its corresponding ideal probability, often calculated via simulation on a classical computer.

[0099] In some embodiments, the readout unit 105 can apply error correction to the output signal before performing the at least one statistical operation. The error correction can be such that it can be applied at this stage based on the measurement results without requiring a quantum operation contingent on the measurement results.

[0100] FIG. 5 illustrates a schematic diagram of the control unit 102 according to one embodiment.

[0101] The control unit 102 may comprise at least one processor 601. The at least one processor 601 may comprise one or more of a variety of processing devices, such as, for example, a coprocessor, a microprocessor, a digital signal processor (DSP), processing circuits with or without an attached DSP, or a variety of other processing devices including 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, and the like.

[0102] The control unit 102 may further comprise a memory 602. The memory 602 may be configured to store, for example, computer programs, etc. The memory 602 may consist of 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 602 may be embodied as a magnetic storage device (such as a hard disk drive, 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.).

[0103] The control unit 102 may further comprise other components not illustrated in the embodiment of Fig. 6. The control unit 102 may, for example, comprise an input / output bus for connecting the control unit 102 to other devices. Furthermore, a user may control the control unit 102 via the input / output bus. A user may, for example, control the quantum computing operations performed by the apparatus 100 via the control unit 102 and the input / output bus.

[0104] The control unit 102 may further comprise suitable signal sources for generating and controlling the control signals 104. For example, the control unit 102 may comprise at least one RF signal source and / or at least one optical signal source, such as at least one laser.

[0105] When the control unit 102 is configured to implement a function, one and / or more components of the control unit 102 may be configured to implement the function, such as the at least one processor 601 and / or the memory 602. Furthermore, when the at least one processor 601 is configured to implement a function, the function may be implemented, for example, using program code provided in the memory.

[0106] The control unit 102 may be implemented at least in part using, for example, a computer, some other computing device, or the like.

[0107] Any range or device value given herein may be extended or modified without losing the effect sought, and any embodiment may be combined with another embodiment unless expressly denied.

[0108] 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 forms of implementing the claims and that other equivalent features and acts are intended to be within the scope of the claims.

[0109] 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 stated problems or have any or all of the stated benefits and advantages. It will be further understood that references to "an" or "an" item may refer to one or more of those items.

[0110] The steps of the methods described herein may be performed in any suitable order, or simultaneously as appropriate. Additionally, individual blocks may be deleted from any of the methods 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 of the other embodiments described to form further embodiments without losing the desired effect.

[0111] The term "comprising" is used herein to mean that the specified methods, blocks, or elements are included, but that such blocks or elements do not constitute an exclusive list and that the method or apparatus may include additional blocks or elements.

[0112] 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 in some detail, or with reference to one or more individual embodiments, those skilled in the art may make numerous modifications to the disclosed embodiments without departing from the spirit or scope of the present specification. [Explanation of symbols]

[0113] 100 Equipment for quantum computing 101 Quantum Computing Unit 102 Control unit 103 Signal distribution device 104 Control Signal 105 Readout unit 106 Output Signal 201 Synchronization Device 202 Tuning Unit 203 Tuning element 301 Delay Line 401 Superconducting Quantum Interference Device (SQUID) 402 Frequency Tuning Element 403 Signal Line 404 Capacitive circuit 405 Cubit 601 Processor 602 Memory

Claims

1. An apparatus (100) for quantum computing, comprising: a plurality of quantum computing units (101), each quantum computing unit comprising a plurality of qubits arranged to perform a quantum computation according to a plurality of control signals provided to said quantum computing unit, and to provide at least one output signal according to a result of said quantum computation; a control unit (102) for providing the plurality of control signals (104) to the plurality of quantum computing units; a signal distribution device (103) for transmitting the plurality of control signals (104) generated from the control unit (102) to the plurality of quantum computing units (101), the signal distribution device (103) being configured to distribute each control signal in the plurality of control signals (104) generated from the control unit (102) to each quantum computing unit in the plurality of quantum computing units (101); a signal distribution device (103) configured by the control unit (102) to cause each quantum computing unit in the plurality of quantum computing units (101) to perform a separate instance of the quantum computation via the plurality of control signals (104) and the signal distribution device (103); obtaining the at least one output signal (106) from each quantum computing unit in the plurality of quantum computing units (101); performing at least one statistical operation based on the output signal (106), thereby obtaining an overall quantum computation result; and a read-out unit (105) configured to:

2. The apparatus (100) of claim 1 , wherein each quantum computing unit in the plurality of quantum computing units (101) corresponds to a quantum processing unit (QPU), a core in a multi-core QPU, or a subunit of a QPU.

3. 3. The apparatus (100) of claim 1 or 2, wherein the signal distribution device (103) is configured to distribute each control signal in the plurality of control signals (104) originating from the control unit (102) to each quantum computing unit in the plurality of quantum computing units (101) using at least one T-junction, at least one power divider, at least one Wilkinson power divider, at least one directional coupler and / or at least one hybrid coupler.

4. 4. The apparatus (100) of claim 1, further comprising a tuning device configured to adjust at least one characteristic of the plurality of control signals distributed by the signal distribution device, the at least one characteristic comprising at least one of frequency, amplitude, phase and / or relative timing.

5. 5. The apparatus (100) of claim 4, wherein the tuning device further comprises at least one voltage-controlled attenuator configured to adjust at least one control signal in the plurality of control signals distributed by the signal distribution device.

6. 6. The apparatus (100) of claim 5, wherein the at least one voltage controlled attenuator comprises at least one high electron mobility transistor, at least one tunable reactive impedance element, at least one superconducting quantum interference device, and / or at least one varactor diode.

7. 7. The apparatus (100) of claim 1, wherein the output signals from the plurality of quantum computing units (101) are time multiplexed, and the readout unit (105) is further configured to obtain the output signal from each quantum computing unit in the plurality of quantum computing units (101) according to the time multiplexing.

8. 8. The apparatus (100) of claim 7, further comprising a delay line coupled to the plurality of quantum computing units (101) and configured to time multiplex the output signals (106) from the plurality of quantum computing units.

9. 9. The apparatus (100) of claim 1, wherein the readout unit (105) further comprises a summing device, and the readout unit (105) is configured to perform the at least one statistical operation based on the output signals (106) by coherently summing the output signals (106) via the summing device.

10. 10. The apparatus (100) of claim 1, wherein each quantum computing unit in the plurality of quantum computing units (101) further comprises a plurality of frequency tuning elements configured to tune a qubit frequency of the plurality of qubits according to a frequency tuning signal.

11. 11. The apparatus (100) of claim 1, wherein each quantum computing unit in the plurality of quantum computing units (101) further comprises a plurality of capacitance tuning elements configured to tune capacitances of the plurality of qubits according to a capacitance tuning signal.

12. 12. The apparatus (100) of any one of claims 1 to 11, wherein the plurality of qubits (405) comprises superconducting qubits.

13. 13. The apparatus (100) of any one of claims 1 to 12, wherein the at least one statistical operation comprises at least one of a mean, a variance and / or a cross-entropy.

14. 14. The apparatus (100) of claim 1, further comprising a cryostat, the plurality of quantum computing units (101) and the signal distribution device (103) being arranged inside the cryostat.

15. 15. A quantum computing system comprising a plurality of devices (100) according to any one of claims 1 to 14.

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