Amazon Technologies, Inc.

Christopher Chamberland

Kyungjoo Noh

Fernando Brandao

Earl Campbell

Patricio Arrangoiz Arriola

Connor Hann

Oskar Jon Painter

Harald Esko Jakob Putterman

Prasahnt Sivarajah

Amir Safavi-Naeini

Joseph Kramer Iverson

Luis Goncalves

Prithviraj Prabhu

Eric Christopher Peterson

Sebastian Johannes Grimberg

Andrew Joseph Keller

Ashley James Milsted

Arne Grimsmo

Colm Andrew Ryan

Matthew Matheny

Menyoung Lee

Noah John Shutty

Thomas Scaffidi

Techniques for optimizing distillation tile layouts for distillation tiles in a magic state factory of a quantum computer and a scheduling of distilled magic state production (e.g., using temporally encoded lattice surgery based (TELS-based) magic state distillation) using said distillation tiles are disclosed. Customized designs for distillation tile layouts that reduce space-time costs when executing a given quantum algorithm are presented, wherein the designs may be customized based, at least in part, on a selected classical error-correcting code and distillation circuit, on a decision whether to perform parallelized TELS-based magic state distillation, etc. Production of distilled magic states may then be configured using a round robin scheduling design in order to minimize potential time in which a processing core of the quantum computer is waiting for another newly distilled magic state from the magic state factory to use for logical computation related to the given quantum algorithm being executed.

Distillation tile layouts and scheduling within a magic state factory for magic state distillation techniques

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 technique for performing lattice surgery without using twists is disclosed. Also, an error correcting code and decoder is provided that allows for error decoding of Pauli measurements performed in association with a lattice surgery operation. This allows for overall run-times of lattice surgery to be reduced. For example, some level of errors are tolerable, because they can be corrected, thus fewer measurement rounds (d) may be performed for a given round of Pauli measurements. Additionally, a temporal encoding of lattice surgery technique is provided, which may additionally or alternatively be used to shorten run times. Also, a quantum computer layout is provided, wherein the layout includes a core computing region and a cache region. Also, protocols for swapping logical qubits between the core and cache are provided.

Quantum computer designs with core computing and cache regions that utilize lattice surgery

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

Lattice surgery techniques without using twists

Techniques for training local decoders for use in a local and global decoding scheme for quantum error correction of circuit-level noise within quantum surface codes such that the decoding schemes have fast decoding throughout and low latency times for quantum algorithms are disclosed. The local decoders may have a neural network architecture and may be trained using training data sets comprising simulated rounds of syndrome measurements for respective simulated quantum surface codes in addition to information such as syndrome differences, qubit placements, and temporal boundaries within the simulated rounds of syndrome measurements in order to train the local decoders for arbitrarily sized quantum surface codes and arbitrary numbers of rounds of syndrome measurements. Following a local decoding stage in which a large number of data errors have been corrected by a local decoder, error correction for remaining errors may continue with a more efficient global decoding stage.

Training neural network local decoders for circuit-level quantum error correction

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

Techniques for implementing a local neural network and global decoding scheme for quantum error correction of circuit-level noise within quantum surface codes such that the decoding schemes have fast decoding throughout and low latency times for quantum algorithms are disclosed. A local neural network decoder may be pre-trained via a supervised learning technique such that the local neural network decoder may be applied for error correction in the presence of circuit-level noise in arbitrarily sized surface codes in a local decoding stage. Prior to a global decoding stage, an intermediate stage may be used to remove vertical pairs of highlighted vertices within the matching graph, which may reduce a syndrome density within the matching graph to allow for faster decoding at the global decoding stage. Such an intermediate stage may include application of a syndrome collapse or vertical cleanup technique.

Treating circuit-level noise using a local and global decoding scheme

A technique for performing lattice surgery using twists is disclosed. Also, an error correcting code and decoder is provided that allows for error decoding of Pauli measurements performed in association with a lattice surgery operation. This allows for overall run-times of lattice surgery to be reduced. For example, some level of errors are tolerable, because they can be corrected, thus fewer measurement rounds (d) may be performed for a given round of Pauli measurements. Additionally, a temporal encoding of lattice surgery technique is provided, which may additionally or alternatively be used to shorten run times. Also, a quantum computer layout is provided, wherein the layout includes a core computing region and a cache region. Also, protocols for swapping logical qubits between the core and cache are provided.

Lattice surgery techniques using twists

Techniques for performing temporally encoded lattice surgery (TELS) protocols to reduce space-time costs of lattice surgery measurements are disclosed. A given quantum algorithm may be represented using Pauli-based computation, and associated multi-qubit Pauli operators may be encoded into codewords of a given classical error-correcting code. A hybrid error detection and correction scheme may then be applied during a given TELS protocol in which classical error syndromes corresponding to errors with weights up to a certain weight limit may be corrected while other classical error syndromes corresponding to errors with higher weights may cause given lattice surgery measurements to be remeasured. The weight limit for the hybrid scheme may be chosen based, at least in part, on a number of codewords used, a size of a parallelizable Pauli set used to represent the quantum algorithm, and a distance parameter of the chosen classical error-correcting code.

Temporally encoded lattice surgery protocols for hybrid error detection and correction schemes

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 technique for merging, via lattice surgery, a color code and a surface code, and subsequentially decoding one or more rounds of stabilizer measurements of the merged code is disclosed. Such a technique can be applied to bottom-up fault-tolerant magic state preparation protocol such that an encoded magic state can be teleported from a color code to a surface code. Decoding the stabilizer measurements of the merged code requires a decoding algorithm specific to the merged code in which error correction involving qubits at the border between the surface and color code portions of the merged code is performed. Error correction involving qubits within the surface code portion and within color code portion, respectively, may additionally be performed. In some cases, the magic state is prepared in a color code via a technique for encoding a Clifford circuit design problem as an SMT decision problem.

Teleporting magic states from a color code to a surface code and decoding a merged surface-color code

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

Error correction decoding techniques for lattice surgery

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.

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Pasadena, CA, United States of America

Christopher Chamberland