Abstract: A decoder apparatus for decoding syndromes of a quantum error correction code, the syndromes comprising measurement data from a quantum computer, the quantum computer comprising an array of qubits including syndrome qubits and data qubits. The decoder apparatus is configured to: receive syndrome index data representative of: a physical location of each of the array of qubits within the quantum computer; and lattice dimensions of the array of qubits; receive the syndromes of the quantum error correction code from the quantum computer; determine physical co-ordinate positions for each of the array of qubits based on the syndrome index data; decode the syndromes of the quantum error correction code using the determined physical co-ordinate positions.

Abstract: A method and apparatus for decoding syndromes of a quantum error correction code is disclosed. The method includes the steps of receiving syndrome data for a plurality of quantum error correction rounds performed on a plurality of qubits; identifying a plurality of first blocks within the syndrome data, wherein each first block has a respective first central block surrounded by one or more respective first buffer blocks; decoding each first block to obtain a first committed correction for each respective first central block; identifying a plurality of second blocks within the syndrome data, wherein each second block comprises at least part of at least one first buffer block; and decoding each second block to obtain a second committed correction for each second block. An apparatus including a plurality of block decoders and a process manager is disclosed.

Abstract: A computer-implemented postselection-free method of initializing qubits in a quantum computer, comprising: preparing at least one data qubit and a plurality of auxiliary qubits in respective initial states, wherein each of the at least one data qubit and the plurality of auxiliary qubits has a respective probability of being prepared with an error; and, performing a plurality of non-measurement multi-qubit quantum logic operations that propagate errors between the at least one data qubit and the plurality of auxiliary qubits so as to reduce the probability of an error affecting the at least one data qubit.

Abstract: An apparatus for a quantum computer comprising a memory device and a converter block, the memory device comprising: a local command module; and a double-buffer-memory module comprising a plurality of pairs of memory modules, each memory module: coupled to the local command module; and configured to store a respective operation for controlling a qubit of the quantum computer; wherein the local command module is configured to: receive an instruction to provide the operation for the qubit; read the operation from a respective one of the plurality of pairs of memory modules indicated by the instruction; and provide the operation to the converter block; wherein the converter block is configured to receive the operation from the memory device and provide digital output pulses, representative of the operation, to an output interface, the output interface configured to provide the digital output pulses to a digital-to-analogue converter for controlling the qubit to perform the operation.

Abstract: A computer-implemented method of selecting a power-optimal compression scheme for transmitting digital control signals from a classical interface of a quantum computer to a quantum processing unit (QPU) of the quantum computer is disclosed. The method involves receiving static and dynamic power consumption values associated with operations performable by the QPU; determining compression schemes implementable by the QPU; calculating total power consumption values associated with receiving and decompressing a representative control signal at the QPU using the compression schemes; and selecting the compression scheme having the lowest total power consumption value. A corresponding method for transmitting control signals from a classical interface of the quantum computer to the QPU is also disclosed in which a compressed control signal is transmitted from the classical interface to the QPU with one or more delays.

Abstract: A computer-implemented method for decoding syndromes of a quantum error correction code, the syndromes comprising measurement data from a quantum computer, the method comprising: receiving syndrome measurement data comprising a plurality of quantum error correction rounds performed on a plurality of qubits; identifying a plurality of non-overlapping first blocks within the syndrome measurement data, wherein: each first block has: a first central block of quantum error corrections rounds; and a first buffer block of quantum error correction rounds, wherein the first buffer block surrounds the first central block, and each first block is surrounded by an interstitial region of quantum error correction rounds; identifying the location of a first set of errors in the plurality of qubits by decoding each first block to provide respective decoded first central blocks and respective decoded first buffer blocks; outputting the location of the first set of errors contained within each decoded first central block.