Abstract: In a method to digitally simulate an evolving quantum state of a qubit register of a quantum computer, the quantum state is represented as a state vector of complex-valued amplitudes, where each amplitude is associated with an individual qubit of the qubit register. A directed acyclic graph defining a set of quantum gates of a quantum-computer program is then received. A linear order for the DAG is constructed by minimizing a partial cost function successively re-computed during construction of the linear order, the partial cost function approximating a cost of transforming the state vector according to a subset of the set of quantum gates applied in the linear order. The state vector is transformed according to the set of quantum gates applied in the linear order, and one or more of the complex-valued amplitudes of the transformed state vector are computationally output.

Abstract: A quantum computing device including a doubly controlled iX (CCiX) circuit. The CCiX circuit may be configured to, in a preparation stage, prepare a plurality of magic states. The CCiX circuit may be further configured to receive a plurality of input qubit states including a first control qubit state, a second control qubit state, and a target qubit state. In an execution stage, the CCiX circuit may be further configured to perform a CCiX operation on the target qubit state at least in part by performing a plurality of local joint measurements. At least a subset of the plurality of local joint measurements may be performed between the plurality of magic states and a plurality of auxiliary qubits. Performing the CCiX operation may further include performing a plurality of remote joint measurements of the input qubit states and a plurality of interface qubits included among the plurality of auxiliary qubits.

Abstract: A quantum computing device is provided, including a table lookup circuit configured to receive a first table lookup input and a second table lookup input. The table lookup circuit may be further configured to perform a first table lookup operation on the first table lookup input and a second table lookup operation on the second table lookup input in parallel such that a combined table lookup output is written to a combined output register. The combined table lookup output may include a plurality of first table lookup output qubits of the first table lookup operation and a plurality of second table lookup output qubits of the second table lookup operation.

Abstract: A method to digitally simulate an evolving quantum state of a qubit register of a quantum computer is enacted in a computer system. The quantum state is represented as an array of complex-valued amplitudes, where each amplitude is associated with an individual qubit of the qubit register, and where the quantum state is separable as a product of the individual quantum states of each qubit. One or more quantum-program instructions corresponding to a quantum circuit are received, and the amplitudes of the array are adjusted to reflect a change in the quantum state pursuant to execution of the quantum circuit, the change preserving the separability of the quantum state as a product of individual quantum states of each qubit. One or more of the adjusted amplitudes are then outputted computationally, in such form as to be receivable as input to a computer program.

Abstract: A computing device is provided, including a processor configured to transmit, to a quantum coprocessor, instructions to encode a Markov decision process (MDP) model as a quantum oracle. The processor may be further configured to train a reinforcement learning model at least in part by transmitting a plurality of superposition queries to the quantum oracle encoded at the quantum coprocessor. Training the reinforcement learning model may further include receiving, from the quantum coprocessor, one or more measurement results in response to the plurality of superposition queries. Training the reinforcement learning model may further include updating a policy function of the reinforcement learning model based at least in part on the one or more measurement results.

Abstract: In a method to digitally simulate an evolving quantum state of a qubit register of a quantum computer, the quantum state is represented as a state vector of complex-valued amplitudes, where each amplitude is associated with an individual qubit of the qubit register. A directed acyclic graph defining a set of quantum gates of a quantum-computer program is then received. A linear order for the DAG is constructed by minimizing a partial cost function successively re-computed during construction of the linear order, the partial cost function approximating a cost of transforming the state vector according to a subset of the set of quantum gates applied in the linear order. The state vector is transformed according to the set of quantum gates applied in the linear order, and one or more of the complex-valued amplitudes of the transformed state vector are computationally output.

Abstract: One aspect of this disclosure relates to a method for operating a quantum computing device. A request to execute a first n-qubit gate on a set of n target qubits is received at the quantum computing device. The receiving a request to execute a first n-qubit gate on a set of n target qubits, the n-qubit gate including one or both of a diagonal gate and a diagonal gate conjugated by a multi-qubit Clifford gate. A set of n interface qubits on which to perform the first n-qubit gate is identified, the set of n interface qubits located remotely from the set of n target qubits. A joint Z-Z measurement is executed on each target qubit and its corresponding interface qubit via a pre-established entanglement. The first n-qubit gate is executed on the set of n interface qubits.

Abstract: A method to digitally simulate an evolving quantum state of a qubit register of a quantum computer is enacted in a computer system. The quantum state is represented as an array of complex-valued amplitudes, where each amplitude is associated with an individual qubit of the qubit register, and where the quantum state is separable as a product of the individual quantum states of each qubit. One or more quantum-program instructions corresponding to a quantum circuit are received, and the amplitudes of the array are adjusted to reflect a change in the quantum state pursuant to execution of the quantum circuit, the change preserving the separability of the quantum state as a product of individual quantum states of each qubit. One or more of the adjusted amplitudes are then outputted computationally, in such form as to be receivable as input to a computer program.

Abstract: One aspect of this disclosure relates to a method for operating a quantum computing device. A request to execute a first n-qubit gate on a set of n target qubits is received. The first n-qubit gate is representable as an m-qubit diagonal gate conjugated by a Clifford gate, where m?n. A set of m interface qubits on which to perform the m-qubit diagonal gate are identified. A Clifford operation is executed on each interface qubit and its corresponding target qubits. The m-qubit diagonal gate is executed on the set of m interface qubits.

Abstract: A method for performing a quantum-logic operation on a quantum computer. The method includes enacting classical pebbling on an initial computation graph G defining the quantum-logic operation; extracting a quantum circuit B based on a sequence of steps obtained from the classical pebbling, that sequence including at least one computation step and at least one measurement-based uncomputation step; executing the quantum circuit B on a qubit register of the quantum computer; recording at least one measurement result of the at least one measurement-based uncomputation step of the quantum circuit B as executed on the qubit register; constructing a clean-up computation graph G? based on the at least one measurement result; enacting reversible pebbling on the clean-up computation graph G?; extracting a quantum circuit B? based on a sequence of steps obtained from the reversible pebbling, that sequence including computation and uncomputation steps; and executing the quantum circuit B? on the qubit register.