Amazon Technologies, Inc.

Yale University

The University of Chicago

Kyungjoo Noh

Christopher Chamberland

Fernando Brandao

Connor Hann

Oskar Jon Painter

Patricio Arrangoiz Arriola

Harald Esko Jakob Putterman

Joseph Kramer Iverson

Steven M Girvin

Liang Jiang

Amir Safavi-Naeini

Michel Devoret

Robert J Schoelkopf, Iii

Earl Campbell

Victor V Albert

Prasahnt Sivarajah

Stefan Krastanov

Andrew Joseph Keller

Chao Shen

Thomas Scaffidi

Filip D Rozpedek

Qian Xu

Chiao-Hsuan Wang

José Lebreuilly

Ashley James Milsted

Arne Grimsmo

Colm Andrew Ryan

Matthew Matheny

Menyoung Lee

Iii Schoelkopf Robert J

Robert J Schoelkopf Iii

Cavity resonators are promising resources for quantum technology, while native nonlinear interactions for cavities are typically too weak to provide the level of quan¬ tum control required to deliver complex targeted operations. Here we investigate a scheme to engineer a target Hamiltonian for photonic cavities using ancilla qubits. By off-resonantly driving dispersively coupled ancilla qubits, we develop an optimized approach to engineering an arbitrary photon-number dependent (PND) Hamiltonian for the cavities while minimizing the operation errors. The engineered Hamiltonian admits various applications including canceling unwanted cavity self-Kerr interac¬ tions, creating higher-order nonlinearities for quantum simulations, and designing quantum gates resilient to noise. Our scheme can be implemented with coupled microwave cavities and transmon qubits in superconducting circuit systems.

Photon-number dependent Hamiltonian engineering for resonators

Systems and methods for implementing a quantum code using cat qubits as data qubits and transmon qubits as ancilla qubits is disclosed. In some embodiments, a three-level transmon is used and Chi-matching is performed to determine dispersive coupling coefficients between the cat qubits and first and second excited states of the transmon qubits, wherein the dispersive coupling coefficients are used to perform gates between the cat data qubits and the transmon ancilla qubits. The Chi-matching determines the dispersive coupling coefficients such that the cat qubits are rotated in a same manner while performing the gates regardless as to whether a given transmon ancilla qubit remains in a second excited state or has decayed to a first excited state.

Quantum codes implemented using cat data qubits and transmon ancilla qubits

Quantum repeaters and network architectures use two concatenated quantum error correction codes to increase the transmission range of quantum information. A block of data qubits collectively encode a second-layer logical qubit according to a second-layer code concatenated with a first-layer code. A first-layer quantum repeater first-layer corrects each data qubit based on a first-layer syndrome extracted therefrom. The first-layer quantum repeater transmits these first-layer-corrected qubits to a second-layer quantum repeater via a quantum communication channel. The first-layer quantum repeater also transmits the first-layer syndromes to the second-layer quantum repeater via a classical communication channel. After extracting a second-layer syndrome from the first-layer-corrected qubits, the second-layer quantum repeater uses the first-layer syndromes and second-layer syndrome to second-layer correct the first-layer-corrected qubits. The first-layer syndromes improve quantum error correction by reducing the number of sec-and-layer stabilizer measurements needed to determine which data qubits have an error.

Quantum repeaters for concatenated quantum error correction, and associated methods

High-fidelity measurements of qubits are achieved by increasing a number of measurements taken by use of a swap operation and a readout qubit, deflating a bosonic qubit for which measurement outcomes are affected by single photon/phonon loss events, deflating a bosonic qubit enabling readout in other basis, and evolving the qubit under a Hamiltonian that couples a mode to be measured to another mode where the Hamiltonian is selected from a three wave mixing interaction, and/or a combination of these techniques.

High-fidelity measurement of bosonic modes

Selective frequency dissipation is implemented that enables cooling of energy gap protected qubits such that excited energy states resulting from heating or other undesired processes are returned to a lower excited energy state or a ground state manifold, thus reducing the probability of errors. Also, the selective frequency dissipation inhibits leakage from the energy gap protected qubits when in the ground state.

Frequency selective photon dissipation for an energy gap protected qubit

A hybrid Bacon-Shor surface code is implemented using a fault tolerant quantum computer comprising hybrid acoustic-electric qubits. A control circuit includes an asymmetrically threaded superconducting quantum interference devices (ATS) that excites phonons in a mechanical resonator by driving a storage mode of the mechanical resonator and dissipates phonons from the mechanical resonator via an open transmission line coupled to the control circuit. The hybrid Bacon-Shor surface code only couples four phononic modes per given ATS, reducing cross-talk as compared to other systems that couple more phononic modes per ATS. Also, measurements are performed such that three parity measurements are taken between a phononic readout mode and a transmon qubit in a given syndrome measurement cycle.

Hybrid bacon-shor surface codes in a concatenated cat-qubit architecture

A fault tolerant quantum computer is implementing using hybrid acoustic-electric qubits. A control circuit includes an asymmetrically threaded superconducting quantum interference devices (ATS) that excites phonons in a mechanical resonator by driving a storage mode of the mechanical resonator and dissipates phonons from the mechanical resonator via an open transmission line coupled to the control circuit, wherein the open transmission line is configured to absorb photons from a dump mode of the control circuit. Filters are included in the control circuit to suppress cross-talk errors. Additionally, frequencies and pump mode detunings for respective multiplexed control circuits are strategically selected to reduce cross-talk errors.

Cross-talk reduction in fault tolerant quantum computing system

Systems and methods for performing bosonic quantum error correction (QEC) using Gottesman-Kitaev-Preskill (GKP) states are provided. An ancilla quantum mechanical oscillator is used to probe Gaussian noise experienced by a data quantum mechanical oscillator without disturbing the state of the data quantum mechanical oscillator. The ancilla quantum mechanical oscillator is initialized with a GKP state and entangled with the state of a data quantum mechanical oscillator to correlate any noise experienced by the data state with the state of the ancilla quantum mechanical oscillator. The states are then disentangled, and momentum and position quadrature operators of the ancilla quantum mechanical oscillator are measured and used to perform QEC on the information stored in the data quantum mechanical oscillator.

Error correction while maintaining bosonic nature of the system

A fault tolerant quantum error correction protocol is implemented for a surface code comprising Gottesman Kitaev Preskill (GKP) qubits. Analog information is determined when measuring position or momentum shifts, wherein the analog information indicates a closeness of the shift to a decision boundary. The analog information is further used to determine confidence values for error corrected measurements from the GKP qubits of the surface code. These confidence values are used to dynamically determine edge weights in a matching graph used to decode syndrome measurements of the surface code, wherein the confidence values are obtained using a maximum-likelihood decoding protocol for two-qubit gates. Space-time correlated edges and other edges are included in the matching graph and weighted based at least in part on confidence values for qubits forming the respective edges.

Edge graph mapping using analog information with dynamically updated weighting factors for a surface GKP code

A fault tolerant quantum error correction protocol is implemented for a surface code comprising Gottesman Kitaev Preskill (GKP) qubits. Analog information is determined when measuring position or momentum shifts, wherein the analog information indicates a closeness of the shift to a decision boundary. The analog information is further used to determine confidence values for error corrected measurements from the GKP qubits of the surface code. These confidence values are used to dynamically determine edge weights in a matching graph used to decode syndrome measurements of the surface code, wherein the confidence values are obtained using a maximum-likelihood decoding protocol for two-qubit gates. Also, a three-level ancilla is used to more reliably squeeze the GKP qunaught states.

Preparation of qunaught states for a surface GKP code using a three (or higher) level ancilla system

A fault tolerant quantum error correction protocol is implemented for a surface code comprising Gottesman Kitaev Preskill (GKP) qubits. Analog information is determined when measuring position or momentum shifts, wherein the analog information indicates a closeness of the shift to a decision boundary. The analog information may further be used to determine confidence values for error corrected measurements from the GKP qubits of the surface code.

Fault-tolerant quantum error correction with a surface GKP code

Extra edges are added to a group of edges for use in decoding syndrome measurements of a surface code implemented using hybrid acoustic-electric qubits. The extra edges include two-dimensional cross-edges and three-dimensional space-time correlated edges that identify correlated errors arising from spurious photon dissipation processes of a multiplexed control circuit that leads to cross-talk between storage modes of a set of the mechanical resonators controlled by the given multiplexed control circuit. Additionally, error probabilities used for edge weighting incorporate error probabilities due to the spurious photon dissipation processes.

Stabilizer measurement decoding using additional edges to identify errors caused by cross-talk

A method of simulating quantum gates includes shifting a Fock basis for the simulation such that the simulation can be performed in a smaller (e.g. truncated) Hilbert dimension space. To shift the Fock basis, non-orthonormalized basis states are first defined. The defined basis states are then orthonormalized to construct orthonormalized shifted Fock basis state. Matrix elements are determined for an operator in the orthonormalized shifted Fock basis and the operator is used to simulate the quantum gate in the shifted Fock basis.

Simulating large cat qubits using a shifted fock basis

A fault tolerant quantum computer is implemented using hybrid acoustic-electric qubits. A control circuit includes an asymmetrically threaded superconducting quantum interference devices (ATS) that excites excite phonons in a mechanical resonator by driving a storage mode of the mechanical resonator and dissipates phonons from the mechanical resonator via an open transmission line coupled to the control circuit, wherein the open transmission line is configured to absorb photons from a dump mode of the control circuit.

Fault-tolerant quantum hardware using hybrid acoustic-electrical qubits

According to some aspects, a quantum information system is provided that includes an ancilla qubit; a qudit coupled to the ancilla qubit, a detector configured to generate a detection result based on a quantum state of the ancilla qubit, and a driving source coupled to the qudit and the ancilla qubit and configured to apply at least one qudit driving signal to the qudit based on the detection result and at least one qubit driving signal to the qudit based on the detection result.

Growing community of inventors

Pasadena, CA, United States of America

Kyungjoo Noh