D-wave Systems Inc.

Socpra Sciences Et Genie S.e.c.

Massachusetts Institute of Technology

University of Toronto

Socpra Sciences Et Genie S.e.c., A/s Transfertech Sherbrooke

Alexandre Blais

Jeremy P Hilton

Alexandre M Zagoskin

Geordie Rose

Mohammad H S Amin

William D Oliver

Daniel A Lidar

Alexander Omelyanchouk

Timothy Duty

Lian-Ao Wu

Simon Gustavsson

Shruti Puri

Roni Winik

Arne Loehre Grimsmo

Agustin Di Paolo

Catherine Leroux

Christian Kraglund Andersen

Arne L Grimsmo

Jerome Bourassa

Nicloas Didier

Baptiste Royer

A system and method provide two-qubit gates and quantum computing circuits built therefrom. Pairs of qubits are inductively or capacitively coupled using a coupler that is driven using an off-resonant microwave drive. By controlling the drive, the ZZ interaction between the qubits can be precisely controlled. In particular, the interaction may be selectively reduced or suppressed, thereby isolating the qubits from each other, or the interaction may be increased to provide fast, controlled-Z, two-qubit gates with high fidelity. Moreover, qubits and couplers may be arranged according to their resonant frequencies into unit cells and replicated to arbitrary size, thereby forming a quantum computer.

Tunable interactions for implementing two-qubit gates, and extensible circuits built therefrom

A quantum circuit called a 'qumon' is provided to cancel unwanted ZZ interaction in a superconducting qubit architecture. The qumon qubit has a high coherence, and a positive anharmonicity that may be tuned to cancel the negative anharmonicity in a coupled qubit, such as a transmon qubit. The qumon has three parallel branches, in which are a shunt capacitor; a Josephson junction having weighted energy level and capacitance; and several Josephson junctions in series. The weight is chosen to provide the desired anharmonicity, and the transverse flux noise and transverse charge noise each decrease in proportion to the number of the Josephson junctions in series. Because unwanted ZZ interactions are canceled, qumon qubits and transmon qubits may be capacitively coupled in an alternating pattern to provide a surface code in which these interactions are canceled in an extensible way.

Cancellation of unwanted interactions in a superconducting quantum architecture

A method and circuit QED implementation of a control-phase quantum logic gate U(&#x3b8;)=diag[1,1,1, e]. Two qubits Q, two resonators R, Rand a modulator. Qand Q, each has a frequency &#x3c9;and characterized by {circumflex over (&#x3c3;)}. Ris associated with Qand defined by a quantum non-demolition (QND) longitudinal coupling g{circumflex over (&#x3c3;)}(&#xe2;&#x2020;+&#xe2;). Ris integrated into R, the QND second longitudinal coupling is defined by Ras g{circumflex over (&#x3c3;)}({circumflex over (b)}&#x2020;+{circumflex over (b)}) or, when Ris integrated into R, the QND second longitudinal coupling is defined by Ras g{circumflex over (&#x3c3;)}(&#xe2;&#x2020;+&#xe2;) The modulator periodically modulates, at a frequency &#x3c9;during a time t, the longitudinal coupling strengths gand gwith respective signals of respective amplitudes {tilde over (g)}and {tilde over (g)}. Selecting a defined value for each of t, gand gdetermines &#x3b8; to specify a quantum logical operation performed by the gate. Qand Qare decoupled when either one of gand gis to set to 0.

Controlled-phase quantum logic gate

A method of quantum processing using a quantum processor comprising a plurality of Kerr non-linear oscillators (KNOs), each operably drivable by both i) a controllable single-boson drive and ii) a controllable two-boson drive, the method comprising simultaneously controlling a drive frequency and a drive amplitude of the controllable single-boson drives to define a problem and controlling a drive frequency and a drive amplitude of the two-photon drives to define the Hilbert space, including increasing the amplitude of the two-boson drive and reaching both amplitude conditions a) 4 times the amplitude of the two-boson drives being greater than the loss rate, and b) the amplitude of the two-boson drives being greater than the amplitude of the single-boson drive, and maintaining both amplitude conditions a) and b) until a solution to the problem is reached; and reading the solution.

Quantum processor, and method of quantum processing

Method and circuit for reading a value {circumflex over (&#x3c3;)}stored in a quantum information unit (qubit) memory having a qubit frequency &#x3c9;, with a resonator defined by a resonator damping rate &#x3ba;, a resonator frequency &#x3c9;, a resonator electromagnetic field characterized by &#xe2;and &#xe2;, a longitudinal coupling strength g, an output &#xe2;and a longitudinal coupling g{circumflex over (&#x3c3;)}(&#xe2;+&#xe2;). At a quantum non-demolition (QND) longitudinal modulator, periodically modulating the longitudinal coupling strength gwith a signal of amplitude {tilde over (g)}at least three (3) times greater than the resonator damping rate &#x3ba; and of frequency &#x3c9;with &#x3c9;+&#x3ba; resonant with &#x3c9;, wherein the longitudinal coupling strength gvaries over time (t) in accordance with g(t)=+{tilde over (g)}cos(&#x3c9;t) withrepresenting an average value of gand at a QND homodyne detector, measuring the value {circumflex over (&#x3c3;)}of the qubit memory from a phase reading of the output {circumflex over (&#x3c3;)}.

Periodical modulation of longitudinal coupling strength for quantum non-demolition qubit readout

A method for reading out the state of a mesoscopic phase device. In the method the mesoscopic phase device is coherently coupled to a mesoscopic charge device using a phase shift device and the quantum state of the mesoscopic charge device is measured. A method for reading out the quantum state of a qubit in a heterogeneous quantum register. The heterogeneous quantum register includes a first plurality of phase qubits and a second plurality of charge qubits. In the method a first phase qubit or a first charge qubit in the heterogeneous quantum register is selected. The first phase qubit or the first charge qubit is coherently connected to a mesoscopic charge device for a duration t. The quantum state of the mesoscopic charge device is read out after the duration thas elapsed.

Quantum phase-charge coupled device

The present invention involves a quantum computing structure, comprising: one or more logical qubits, which is encoded into a plurality of superconducting qubits; and each of the logical qubits comprises at least one operating qubit and at least one ancilla qubit. Also provided is a method of quantum computing, comprising: performing encoded quantum computing operations with logical qubits that are encoded into superconducting operating qubits and superconducting ancilla qubits. The present invention further involves a method of error correction for a quantum computing structure comprising: presenting a plurality of logical qubits, each of which comprises an operating physical qubit and an ancilla physical qubit, wherein the logical states of the plurality of logical qubits are formed from a tensor product of the states of the operating and ancilla qubits; and wherein the states of the ancilla physical qubits are suppressed; and applying strong pulses to the grouping of logical qubits.

Encoding and error suppression for superconducting quantum computers

A method for performing a single-qubit gate on an arbitrary quantum state. An ancillary qubit is set to an initial state |I&#x3e;. The data qubit is coupled to an ancillary qubit. The state of the ancillary qubit is measured, and the data qubit and the ancillary qubit are coupled for a first period of time. A method for applying a single-qubit gate to an arbitrary quantum state. A state of a first and second ancillary qubit are set to an entangled initial state |I&#x3e;. A state of a data qubit and the first ancillary qubit are measured thereby potentially performing a single qubit operation on the arbitrary quantum state. A first result is determined. The first result indicates whether the single qubit operation applied the single qubit gate to the arbitrary quantum state.

Methods for single qubit gate teleportation

A solid-state quantum computing qubit includes a multi-terminal junction coupled to a superconducting loop where the superconducting loop introduces a phase shift to the superconducting order parameter. The ground state of the supercurrent in the superconducting loop and multi-terminal junction is doubly degenerate, with two supercurrent ground states having distinct magnetic moments. These quantum states of the supercurrents in the superconducting loop create qubits for quantum computing. The quantum states can be initialized by applying transport currents to the external leads. Arbitrary single qubit operations may be performed by varying the transport current and/or an externally applied magnetic field. Read-out may be performed using direct measurement of the magnetic moment of the qubit state, or alternatively, radio-frequency single electron transistor electrometers can be used as read-out devices when determining a result of the quantum computing. Further, qubits as described above can form arrays of qubits for performing controlled quantum computing calculations. In one example, an array of qubits can be utilized as a random number generator.

Quantum bit with a multi-terminal junction and loop with a phase shift

A circuit comprising a superconducting qubit and a resonant control system that is characterized by a resonant frequency. The resonant frequency of the control system is a function of a bias current. The circuit further includes a superconducting mechanism having a capacitance or inductance. The superconducting mechanism coherently couples the superconducting qubit to the resonant control system. A method for entangling a quantum state of a first qubit with the quantum state of a second qubit. In the method, a resonant control system, which is capacitively coupled to the first and second qubit, is tuned to a first frequency that corresponds to the energy differential between the lowest two potential energy levels of the first qubit. The resonant control system is then adjusted to a second frequency corresponding to energy differential between the lowest two potential energy levels of the second qubit.

Resonant controlled qubit system

A method is provided for entangling a quantum state of a qubit with a quantum state of a resonant control system. The method comprises tuning the resonant control system, which is capacitively or inductively coupled to the qubit, to a resonant frequency for a period of time. The resonant frequency corresponds to an energy difference between a first energy level of the qubit and a second energy level of the qubit. The act of tuning entangles the quantum state of the qubit with the quantum state of the resonant control system. A representative resonant control system includes a Josephson junction. A method is also provided for entangling a quantum state of a qubit, within a plurality of qubits, with a quantum state of a resonant control system.

Methods for coupling a superconducting qubit to a resonant control circuit. An interaction term between the qubit and the circuit initially has a diagonal component. A recoupling operation is applied to the qubit. The circuit is tuned so that a frequency of the qubit and circuit match. A second recoupling operation transforms the term to have only off-diagonal components. A method for entangling a state of two qubits coupled to a bus with a control circuit. An interaction term between at least one of the qubits and the circuit has a diagonal component. A recoupling operation is applied to at least one of the qubits such that the term has only off-diagonal components. The frequency of the circuit is tuned to the frequency of the first qubit, and then tuned to the frequency of the second qubit. The recoupling operation is reapplied to at least one of the qubits.

Growing community of inventors

Sherbrooke, Canada

Alexandre Blais