Abstract: A method is presented for controlling a spin system in an external magnetic field. The method includes sending a first pulse to a resonator over a first period. The resonator generates a magnetic field in response to receiving the first pulse. Moreover, the resonator applies the magnetic field to the spin system and the first pulse maintains the magnetic field in a transient state during the first period. The method also includes sending a second pulse to the resonator over a second period immediately following the first period. The resonator alters a magnitude of the magnetic field to zero in response to receiving the second pulse. Other methods are presented for controlling a spin system in an external magnetic field, including systems for controlling a spin system in an external field.

Abstract: For reading out a state of a qubit, a readout input waveform is injected into a system that comprises an information storage element for storing the state of the qubit and a readout resonator that is electromagnetically coupled to said information storage element. A readout output waveform is extracted from said system and detected. The injection of the readout input waveform takes place through an excitation port that is also used to inject excitation waveforms to the information storage element for affecting the state of the qubit. A phase of the readout input waveform is controllably shifted in the course of injecting it into the system.

Abstract: According to one embodiment, a calculating device includes nonlinear oscillators, connectors, and a controller. One of the connectors connects at least two of the nonlinear oscillators. The nonlinear oscillators include first and second nonlinear oscillators. The first nonlinear oscillator includes a first circuit part and a first conductive member. The first circuit part includes first and second Josephson junctions. The second nonlinear oscillator includes a second circuit part and a second conductive member. The second circuit part includes third and fourth Josephson junctions. Numbers of the connectors connected to the first and second connectors are first and second numbers, respectively. The second number is greater than the first number. The controller performs at least a first operation of supplying a first signal to the first conductive member and supplying a second signal to the second conductive member. The second signal is different from the first signal.

Abstract: Various embodiments of a phononic system to achieve quantum-analogue phase-based unitary operations are disclosed. A plurality of diatomic molecules is adsorbed on a cubic crystal surface. At least a first pair of parallel chains is created from the plurality of diatomic molecules, such that the two constituent chains of the first pair of parallel chains each comprise three or more diatomic molecules. One or more diatomic molecules of the first pair of parallel chains are displaced in order to thereby create one or more kinks in the first pair of parallel chains. The one or more kinks apply a first desired phase transformation to elastic waves scattered by the plurality of diatomic molecules and adjusting the number of kinks or adjusting the order in which kinks are created or modified causes a corresponding adjustment to the first desired phase transformation.

Abstract: Systems and methods are provided for flux control of a qubit. A quantum system includes a microwave transmitter configured to provide a continuous microwave tone, and a qubit configured such that transition energy of the qubit between a ground state of the qubit and a first excited state of the qubit is tunable via an applied flux. The qubit also has an inductive element responsive to the continuous microwave tone to produce a Rabi oscillation within the qubit. A flux source is configured to apply a flux to the qubit to selectively tune the transition energy of the qubit, such that the transition energy of the qubit can be tuned to a frequency of the Rabi oscillation or detuned from the Rabi oscillation.

Abstract: Superconducting circuits for processing input signals are described. An example superconducting circuit includes a first portion configured to receive an input signal having a data pattern represented by edge transitions in the input signal. The superconducting circuit further includes a second portion configured to provide an output signal, where the superconducting circuit is configured to, without applying a direct-current (DC) offset to the input signal, output the output signal corresponding to the edge transitions such that the output signal is substantially representative of the data pattern despite not applying the DC offset to the input signal.

Abstract: Methods, systems, and apparatus for individual qubit excitation control with a global excitation drive. In one aspect, a method includes accessing a quantum system that comprises a plurality of qubits; a plurality of qubit frequency control lines, each qubit frequency control line corresponding to an individual qubit and controlling the frequency of the qubit; a driveline; a plurality of couplers, each coupler coupling a corresponding qubit to the driveline so that a plurality of qubits are coupled to the driveline; determining one or more qubits that require a rotation operation; for each qubit requiring a rotation operation: tuning the qubit frequency to the corresponding driveline frequency of the rotation operation; performing the rotation operation using a microwave pulse on the excitation drive; and tuning the qubit away from the driveline frequency of the rotation operation.

Abstract: Methods and apparatuses are provided for controlling the state of a qubit. A qubit apparatus includes a load, a qubit, and a compound Josephson junction coupler coupling the qubit to the load. A coupling controller controls the coupling strength of the compound Josephson junction coupler such that a coupling between the qubit and the load is a first value when a reset of the qubit is desired and a second value during operation of the qubit.

Abstract: In some aspects, a control system interacts with a quantum system. In some instances, the quantum system includes qubits that respond to a control signal generated by the control system, and the control system is configured to generate the control signal in response to an input signal. A control sequence (which may include, for example, a sequence of values for the input signal) can be generated by a computing system based on a target operation to be applied to the qubits. The control sequence can be generated based on the target operation, a quantum system model, a distortion model and possibly other information. The quantum system model represents the quantum system and includes a control parameter representing the control signal. The distortion model represents a nonlinear relationship between the control signal and the input signal. The control sequence is applied to the quantum system by operation of the control system.

Abstract: The disclosed technology concerns tools and techniques for implementing error-correction codes in a quantum computing device. In particular embodiments, Majorana fermion stabilizer codes having small numbers of modes and distance are disclosed. Particular embodiments have an upper bound on the number of logical qubits for distance 4 codes, and Majorana fermion codes are constructed that saturate this bound. Other distance 4 and 6 codes are also disclosed.

Abstract: A device in accordance with several embodiments can include a plurality of N Superconducting Quantum Interference Devices (SQUIDs), which can be divided into a plurality of sub-blocks of SQUIDs. The SQUIDs in the sub-blocks can be RF SQUIDs, DC SQUIDs or bi-SQUIDs. The sub-blocks can be arranged in a plurality of X tiers, with each Ti tier having a different number of sub-blocks of SQUIDs than an immediately adjacent Ti tier. Each Ti tier can have the same total bias current; and can have SQUIDs with different critical currents and loop sizes, with the different loop sizes on each tier having a Gaussian distribution of between 0.5 and 1.5 (or a random distribution). Additionally, the Arrays can be configured as three independent planar arrays of SQUIDs. The three planar arrays can be triangular when viewed in top plan, and can be arranged so that they are orthogonal to each other.

Abstract: A system for locating errors for quantum computing includes an interface, a shift array, a comparison block, a tree pipeline, and a serializer. The interface is configured to receive a set of quantum bit values, wherein the set of quantum bit values comprise a subset of quantum bit values in a quantum bit array. The shift array is configured to store a prior set of quantum bit values read from identical quantum bit locations at a prior time corresponding to the set of quantum bit values. The comparison block is configured to identify differences between the set of quantum bit values and the prior set of quantum bit values. The tree pipeline configured to rank the differences identified. The serializer is configured to serialize the differences identified in order by rank.

Abstract: One embodiment includes a superconducting gate memory circuit. The circuit includes a Josephson D-gate circuit configured to set a digital state as one of a first data state and a second data state in response to a write enable single flux quantum (SFQ) pulse provided on a write enable input and a respective presence of or absence of a write data SFQ pulse provided on a data write input. The circuit also includes a storage loop coupled to the Josephson D-gate. The storage loop can be configured to store the digital state and to readout the digital state at an output in response to a read enable SFQ pulse provided on a read enable input and a read data SFQ pulse provided on a read data input.

Abstract: In a general aspect, control of a quantum superconducting circuit is analyzed. In some implementation, a parameter set for a control signal for a superconducting quantum circuit is received. The parameters set can include initial voltage amplitudes for respective time segments of the control signal. A first subset of time segments is selected for improving a quality measure of a quantum logic operation produced by delivery of the control signal in the superconducting quantum circuit. New voltage amplitudes are calculated for one or more segments in the first subset, such that the new voltage amplitudes improve the quality measure. The parameter set is updated to include the new voltage amplitudes for the first subset while preserving the initial voltage amplitudes for a second subset of the time segments.

Abstract: An isochronous receiver system is provided and includes a single flux quantum (SFQ) receiver to receive a data signal from a transmission line. The single flux quantum receiver then converts the data signal to an SFQ signal. The system also includes a converter system to convert the SFQ signal to a reciprocal quantum logic (RQL) signal and to phase-align the RQL signal with a sampling phase of an AC clock signal.

Abstract: Systems and methods are provided for a tunable transmon qubit. The qubit includes a first Josephson junction on a first path between a transmission line and a circuit ground and second and third Josephson junctions arranged in parallel with one another on a second path between the transmission line and the circuit ground to form a direct current superconducting quantum interference device (DC SQUID). The DC SQUID is in parallel with the first Josephson junction. A capacitor is arranged in parallel with the first Josephson junction and the DC SQUID on a third path between the transmission line and the circuit ground as to form, in combination with the first path, an outer loop of the tunable transmon qubit. A bias circuit is configured to provide a constant bias flux to one of the DC SQUID and the outer loop of the tunable transmon qubit.

Abstract: A logic device is provided which includes an electron monochromator. The electron monochromator includes a quantum dot disposed between first and second tunneling barriers, an emitter coupled to the first tunneling barrier, and a collector coupled to the second tunneling barrier. The logic device also includes a quantum interference device. The quantum interference device includes a source which is coupled to the collector of the electron monochromator.

Abstract: A device includes a housing, at least two qubits disposed in the housing and a resonator disposed in the housing and coupled to the at least two qubits, wherein the at least two qubits are maintained at a fixed frequency and are statically coupled to one another via the resonator, wherein energy levels |03> and |12> are closely aligned, wherein a tuned microwave signal applied to the qubit activates a two-qubit phase interaction.

Abstract: A quantum computer may include topologically protected quantum gates and non-protected quantum gates, which may be applied to topological qubits. The non-protected quantum gates may be implemented with a partial interferometric device. The partial interferometric device may include a Fabry-Pérot double point contact interferometer configured to apply “partial” interferometry to a topological qubit.

Abstract: Systems and methods for reading out the states of superconducting flux qubits may couple magnetic flux representative of a qubit state to a DC-SQUID in a variable transformer circuit. The DC-SQUID is electrically coupled in parallel with a primary inductor such that a time-varying (e.g., AC) drive current is divided between the DC-SQUID and the primary inductor in a ratio that is dependent on the qubit state. The primary inductor is inductively coupled to a secondary inductor to provide a time-varying (e.g., AC) output signal indicative of the qubit state without causing the DC-SQUID to switch into a voltage state. Coupling between the superconducting flux qubit and the DC-SQUID may be mediated by a routing system including a plurality of latching qubits. Multiple superconducting flux qubits may be coupled to the same routing system so that a single variable transformer circuit may be used to measure the states of multiple qubits.

Abstract: Computing bus devices that enable quantum information to be coherently transferred between conventional qubit pairs are disclosed. A concrete realization of such a quantum bus acting between conventional semiconductor double quantum dot qubits is described. The disclosed device measures the joint (fermion) parity of the two qubits by using the Aharonov-Casher effect in conjunction with an ancillary superconducting flux qubit that facilitates the measurement. Such a parity measurement, together with the ability to apply Hadamard gates to the two cubits, allows for the production of states in which the qubits are maximally entangled, and for teleporting quantum states between the quantum systems.

Abstract: Computing bus devices that enable quantum information to be coherently transferred between topological and conventional qubits are disclosed. A concrete realization of such a topological quantum bus acting between a topological qubit in a Majorana wire network and a conventional semiconductor double quantum dot qubit is described. The disclosed device measures the joint (fermion) parity of the two different qubits by using the Aharonov-Casher effect in conjunction with an ancillary superconducting flux qubit that facilitates the measurement. Such a parity measurement, together with the ability to apply Hadamard gates to the two qubits, allows for the production of states in which the topological and conventional qubits are maximally entangled, and for teleporting quantum states between the topological and conventional quantum systems.

Abstract: Systems and methods for reading out the states of superconducting flux qubits may couple magnetic flux representative of a qubit state to a DC-SQUID in a variable transformer circuit. The DC-SQUID is electrically coupled in parallel with a primary inductor such that a time-varying (e.g., AC) drive current is divided between the DC-SQUID and the primary inductor in a ratio that is dependent on the qubit state. The primary inductor is inductively coupled to a secondary inductor to provide a time-varying (e.g., AC) output signal indicative of the qubit state without causing the DC-SQUID to switch into a voltage state. Coupling between the superconducting flux qubit and the DC-SQUID may be mediated by a routing system including a plurality of latching qubits. Multiple superconducting flux qubits may be coupled to the same routing system so that a single variable transformer circuit may be used to measure the states of multiple qubits.

Abstract: A system for performing digital operations, including a first device configured to transform a digital input into one or more signals, at least one AB ring, the at least one AB ring irreducibly-coupled and configured to include at least three terminals, a second device configured to read a portion of a signal expressed upon two or more of the at least three terminals, and a third device configured to transform the portion of the signal expressed upon two or more of the at least three terminals into a digital output, the third device operationally connected to the second device.

Abstract: Analog processors for solving various computational problems are provided. Such analog processors comprise a plurality of quantum devices, arranged in a lattice, together with a plurality of coupling devices. The analog processors further comprise bias control systems each configured to apply a local effective bias on a corresponding quantum device. A set of coupling devices in the plurality of coupling devices is configured to couple nearest-neighbor quantum devices in the lattice. Another set of coupling devices is configured to couple next-nearest neighbor quantum devices. The analog processors further comprise a plurality of coupling control systems each configured to tune the coupling value of a corresponding coupling device in the plurality of coupling devices to a coupling. Such quantum processors further comprise a set of readout devices each configured to measure the information from a corresponding quantum device in the plurality of quantum devices.

Abstract: A quantum processor may employ a heterogeneous qubit-coupling architecture to reduce the average number of intermediate coupling steps that separate any two qubits in the quantum processor, while limiting the overall susceptibility to noise of the qubits. The architecture may effectively realize a small-world network where the average qubit has a low connectivity (thereby allowing it to operate substantially quantum mechanically) but each qubit is within a relatively low number of intermediate coupling steps from any other qubit. To realize such, some of the qubits may have a relatively high connectivity, and may thus operate substantially classically.

Abstract: Analog processors for solving various computational problems are provided. Such analog processors comprise a plurality of quantum devices, arranged in a lattice, together with a plurality of coupling devices. The analog processors further comprise bias control systems each configured to apply a local effective bias on a corresponding quantum device. A set of coupling devices in the plurality of coupling devices is configured to couple nearest-neighbor quantum devices in the lattice. Another set of coupling devices is configured to couple next-nearest neighbor quantum devices. The analog processors further comprise a plurality of coupling control systems each configured to tune the coupling value of a corresponding coupling device in the plurality of coupling devices to a coupling. Such quantum processors further comprise a set of readout devices each configured to measure the information from a corresponding quantum device in the plurality of quantum devices.

Abstract: In one embodiment, the disclosure relates to a method and apparatus for controlling the energy state of a qubit by bringing the qubit into and out of resonance by coupling the qubit to a flux quantum logic gate. The qubit can be in resonance with a pump signal, with another qubit or with some quantum logic gate. In another embodiment, the disclosure relates to a method for controlling a qubit with RSFQ logic or through the interface between RSFQ and the qubit.

Abstract: In one embodiment, the disclosure relates to a method and apparatus for controlling the energy state of a qubit by bringing the qubit into and out of resonance by coupling the qubit to a flux quantum logic gate. The qubit can be in resonance with a pump signal, with another qubit or with some quantum logic gate. In another embodiment, the disclosure relates to a method for controlling a qubit with RSFQ logic or through the interface between RSFQ and the qubit.

Abstract: A system for communicably coupling between two superconducting qubits may include an rf-SQUID coupler having a loop of superconducting material interrupted by a compound Josephson junction and a first magnetic flux inductor configured to controllably couple to the compound Josephson junction. The loop of superconducting material may be positioned with respect to a first qubit and a second qubit to provide respective mutual inductance coupling therebetween. The coupling system may be configured to provide ferromagnetic coupling, anti-ferromagnetic coupling, and/or zero coupling between the first and second qubits. The rf-SQUID coupler may be configured such that there is about zero persistent current circulating in the loop of superconducting material during operation.

Abstract: The disclosure generally relates to a method and apparatus for providing high-speed, low signal power amplification. In an exemplary embodiment, the disclosure relates to a method for providing a wideband amplification of a signal by forming a first transmission line in parallel with a second transmission line, each of the first transmission line and the second transmission line having a plurality of superconducting transmission elements, each transmission line having a transmission line delay; interposing a plurality of amplification stages between the first transmission line and the second transmission line, each amplification stage having an resonant circuit with a resonant circuit delay; and substantially matching the resonant circuit delay for at least one of the plurality of amplification stages with the transmission line delay of at least one of the superconducting transmission lines.

Abstract: A quantum logic gate is formed from multiple qubits coupled to a common resonator, wherein quantum states in the qubits are transferred to the resonator by transitioning a classical control parameter between control points at a selected one of slow and fast transition speeds, relative to the characteristic energy of the coupling, whereby a slow transition speed exchanges energy states of a qubit and the resonator, and a fast transition speed preserves the energy states of a qubit and the resonator.

Abstract: In one embodiment, the disclosure relates to a method and apparatus for controlling the energy state of a qubit by bringing the qubit into and out of resonance by coupling the qubit to a flux quantum logic gate. The qubit can be in resonance with a pump signal, with another qubit or with some quantum logic gate. In another embodiment, the disclosure relates to a method for controlling a qubit with RSFQ logic or through the interface between RSFQ and the qubit.

Abstract: A structure comprising (i) a first information device, (ii) a second information device, (iii) a first coupling element and (iv) a second coupling element is provided. The first information device has at least a first lobe and a second lobe that are in electrical communication with each other. The second information device and has at least a first lobe and a second lobe that are in electrical communication with each other. The first coupling element inductively couples the first lobe of the first information device to the first lobe of the second information device. The second coupling element inductively couples the first lobe of the first information device to the second lobe of the second information device.

Abstract: Apparatus, articles and methods relate to anti-symmetric superconducting devices for coupling superconducting qubits.

Abstract: A transverse coupling system may include a first qubit, a second qubit, a first conductive path capacitively connecting the first qubit and the second qubit, a second conductive path connecting the first qubit and the second qubit, and a dc SQUID connecting the first and the second conductive paths wherein the compound junction loop is threaded by an amount of magnetic flux.

Abstract: Analog processors for solving various computational problems are provided. Such analog processors comprise a plurality of quantum devices, arranged in a lattice, together with a plurality of coupling devices. The analog processors further comprise bias control systems each configured to apply a local effective bias on a corresponding quantum device. A set of coupling devices in the plurality of coupling devices is configured to couple nearest-neighbor quantum devices in the lattice. Another set of coupling devices is configured to couple next-nearest neighbor quantum devices. The analog processors further comprise a plurality of coupling control systems each configured to tune the coupling value of a corresponding coupling device in the plurality of coupling devices to a coupling. Such quantum processors further comprise a set of readout devices each configured to measure the information from a corresponding quantum device in the plurality of quantum devices.

Abstract: A scanning SQUID microscope is set forth to provide improved output imaging. The SQUID microscope includes a vertically adjustable housing adapted to securely retain a SQUID loop or sensor. A scanning stage of the SQUID microscope is adapted to support a sample while moving the sample along a predetermined path to selectively position predetermined portions of the sample in close proximity to the SQUID loop or sensor to permit the loop or sensor to detect predetermined magnetic field information provided by the predetermined portions of the sample. A position control processor coupled to the scanning stage is operative to receive and process the predetermined magnetic field information to provide corresponding position noise information. Criteria are also presented for determining the expected level of position noise under given experimental conditions.

Abstract: A scanning SQUID microscope for acquiring spatially resolved images of physical properties of an object includes a SQUID sensor arranged in perpendicular to the plane of the object under investigation for detecting tangential component of the magnetic field generated by the object. During scanning of the SQUID sensor over the object under investigation, the position signal from a position interpreting unit, as well as relevant output signals from the SQUID sensor are processed by a processing unit which derives from the data, spatially resolved images of the physical properties of the object. The specific orientation of the SQUID sensor with respect to the plane of the object permits an enlarged area of the SQUID chip on which the modulation and feedback line can be fabricated in the same technological process with the SQUID sensor. Additionally, larger contact pads afforded provide for lower contact resistance and ease in forming contact with bias and read-out wires.

Abstract: A rapid single-flux-quantum RSFQ logic circuit includes a first circuit portion having a first end grounded and having in-series connected first and second Josephson junctions. A second circuit portion has a first end grounded and has in-series connected third and fourth Josephson junctions. A first inductance element connects a second end of the first circuit portion to a second end of the second circuit portion. A tap is provided in the first inductance element, an input current signal being supplied to the tap. A bias current source is connected to a first connection node between the first and second Josephson junctions. A second inductance element connects the first connection node to a second connection node between the third and fourth Josephson junctions. A superconducting quantum interference device has fifth and sixth Josephson junctions and is coupled to the second inductance element through a magnetic field.

Abstract: The level of bias current (12) required by a superconductor integrated circuit (2 & 4) is lowered by separating the circuit into portions having separate ground planes and supplying the bias current to the circuit portion (2) in one ground plane in series (10) with that for the circuit portion (4) in another ground plane. To maintain DC isolation between those circuit portions, SFQ pulses inputted (SFQ IN) move across the separate ground planes through a pair of inductively coupled SQUIDS (3 & 5) that define a DC transformer; and a combiner (7) reconstitutes and outputs the SFQ pulses. To provide inductive coupling the DC transformer includes a primary (25) and isolated secondary (5) winding.

Abstract: Disclosed is a superconducting device comprising a logic SQUID and a readout SQUID magnetically coupled with the logic SQUID, which are fabricated using a single layer of an oxide high-temperature superconductor, wherein the logic SQUID comprising a superconducting loop constituted by a first superconducting line, a second superconducting line arranged to be parallel to the first superconducting line, third and fourth superconducting lines provided to connect the first and second superconducting lines, and two Josephson junctions formed in the third and fourth superconducting lines, and widths W.sub.1 and W.sub.2 of the first and second superconducting lines are larger than a distance d between them, the width W.sub.2 is larger than the width W.sub.1, and the widths W.sub.1 and W.sub.2 are larger than the widths W.sub.3 and W.sub.4 of the third and fourth superconducting lines.