Amazon Technologies, Inc.

Fernando Brandao

Christopher Chamberland

Kyungjoo Noh

Connor Hann

Oskar Jon Painter

Earl Campbell

Patricio Arrangoiz Arriola

Joseph Kramer Iverson

Harald Esko Jakob Putterman

Amir Safavi-Naeini

Liang Jiang

Prasahnt Sivarajah

Andrew Joseph Keller

Colm Andrew Ryan

Matthew Matheny

Menyoung Lee

Thomas Scaffidi

Qian Xu

Ashley James Milsted

Arne Grimsmo

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

A Toffoli magic state to be injected in preparation of a Toffoli gate may be prepared using a bottom-up approach. In the bottom-up approach, computational basis states are prepared in a fault tolerant manner using a STOP algorithm. The computational basis states are further used to prepare the Toffoli magic state. The STOP algorithm tracks syndrome outcomes and can be used to determine when to stop repeating syndrome measurements such that faults are guaranteed to be below a threshold level. Also, the STOP algorithm may be used in growing repetition code from a first code distance to a second code distance, such as for use in the computational basis states.

Toffoli gate preparation for a quantum hardware system comprising hybrid acoustic-electrical qubits

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 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

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 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.

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Pasadena, CA, United States of America

Fernando Brandao