Abstract: An apparatus and method are provided for storing and processing quantum information. More particularly, a physical layout is provided to perform Floquet codes. The physical layout includes a quantum processor having an array of qubits (e.g., columns of tetrons or hexons in which Majorana zero modes are located on topological superconductor segments) with a gateable semiconductor devices forming interference loops to perform two-qubit Pauli measurements. Coherent links between qubits in a column enable certain two-qubit Pauli measurements, especially those additional two-qubit Pauli measurements used at a boundary surrounding a region of the bulk code. The two-qubit Pauli measurements are selected to minimize a size of the interference loops. Certain embodiments perform Floquet codes in six time steps. Hexagon embodiments tile the array of qubits with unit cells of 6-gon vertical (or horizontal) bricks. Square-octagon embodiments tile the array of qubits with unit cells of two 4-gon and two 8-gon bricks.

Abstract: A method for simulating a quantum-capacitance response of a material configuration comprises (a) constructing a non-interacting Hamiltonian for the material configuration based on input data; (b) computing a natural-orbitals basis for each of a plurality of parts of the material configuration under the non-interacting Hamiltonian; (c) projecting the non-interacting Hamiltonian in the natural-orbitals basis to obtain a non-interacting quantum-mechanical description for each part; (d) constructing an interacting Hamiltonian by adding an electron-interaction term to the non-interacting Hamiltonian for each of the plurality of parts; (e) for each of a plurality of representative points in a sample space of at least one tunable parameter of the material configuration, using a sums-of-Gaussians procedure to assemble a basis of Gaussian states for approximating low-energy eigenstates of the material configuration under the interacting Hamiltonian; (f) for each of a plurality of vicinities of representative points in

Abstract: Quantum devices formed from a single superconducting wire having a configurable ground connection are described. An example quantum device, configurable to be grounded, comprises a single superconducting wire having at least a first section and a second section, each of which is configurable to be in a topological phase and at least a third section configurable to be in a trivial phase. The quantum device further comprises semiconducting regions formed adjacent to the single superconducting wire, where the single superconducting wire is configurable to store quantum information in at least four Majorana zero modes (MZMs). The semiconducting regions formed adjacent to the single superconducting wire may be used to measure quantum information stored in the at least four MZMs.

Abstract: Quantum devices with chains of quantum dots for controlling tunable couplings between Majorana zero modes (MZMs) are described. Methods for controlling tunable couplings between MZMs using such chains of quantum dots are also described. An example quantum device comprises at least one superconducting island configurable to support at least one pair of Majorana zero modes (MZMs). The quantum device may further include a region adjacent to at least one MZM of the at least one pair of MZMs, where the region is configurable to realize a chain of quantum dots for controlling a tunable coupling between the at least one MZM of the at least one pair of MZMs and another MZM.

Abstract: Quantum devices with two-sided or single-sided dual-purpose Majorana zero mode (MZM) junctions are described. An example quantum device comprises at least one superconducting island configurable to support at least one pair of Majorana zero modes (MZMs). The quantum device further includes a first conductor configurable to be coupled with at least one MZM of the at least one pair of MZMs, where the first conductor is configurable to be in at least one of a grounded state or a Coulomb blockade state. The quantum device further includes a second conductor configurable to be coupled with the at least one MZM of the at least one pair of MZMs, where the second conductor is configurable to be in at least one of a grounded state or a Coulomb blockade state.

Abstract: An apparatus and method are provided for storing and processing quantum information. More particularly, a physical layout is provided to perform Floquet codes. The physical layout includes a quantum processor having an array of qubits (e.g., columns of tetrons or hexons in which Majorana zero modes are located on topological superconductor segments) with a gateable semiconductor devices forming interference loops to perform two-qubit Pauli measurements. Coherent links between qubits in a column enable certain two-qubit Pauli measurements, especially those additional two-qubit Pauli measurements used at a boundary surrounding a region of the bulk code. The two-qubit Pauli measurements are selected to minimize a size of the interference loops. Certain embodiments perform Floquet codes in six time steps. Hexagon embodiments tile the array of qubits with unit cells of 6-gon vertical (or horizontal) bricks. Square-octagon embodiments tile the array of qubits with unit cells of two 4-gon and two 8-gon bricks.

Abstract: A computing system is provided, including a processor configured to identify a plurality of measurement sequences that implement a logic gate. Each measurement sequence may include a plurality of measurements of a quantum state of a topological quantum computing device. The processor may be further configured to determine a respective estimated total resource cost of each measurement sequence of the plurality of measurement sequences. The processor may be further configured to determine a first measurement sequence that has a lowest estimated total resource cost of the plurality of measurement sequences. The topological quantum computing device may be configured to implement the logic gate by applying the first measurement sequence to the quantum state.

Abstract: A computing system is provided, including a processor configured to identify a plurality of measurement sequences that implement a logic gate. Each measurement sequence may include a plurality of measurements of a quantum state of a topological quantum computing device. The processor may be further configured to determine a respective estimated total resource cost of each measurement sequence of the plurality of measurement sequences. The processor may be further configured to determine a first measurement sequence that has a lowest estimated total resource cost of the plurality of measurement sequences. The topological quantum computing device may be configured to implement the logic gate by applying the first measurement sequence to the quantum state.

Abstract: A computing system is provided, including a processor configured to identify a plurality of measurement sequences that implement a logic gate. Each measurement sequence may include a plurality of measurements of a quantum state of a topological quantum computing device. The processor may be further configured to determine a respective estimated total resource cost of each measurement sequence of the plurality of measurement sequences. The processor may be further configured to determine a first measurement sequence that has a lowest estimated total resource cost of the plurality of measurement sequences. The topological quantum computing device may be configured to implement the logic gate by applying the first measurement sequence to the quantum state.

Abstract: A computing device including a processor configured to simulate a quantum device at least in part by receiving a single-particle Hamiltonian matrix that describes an initial Hamiltonian operator. The initial Hamiltonian operator may model a plurality of parts of a quantum device. Simulating the quantum device may further include estimating a reduced density matrix associated with a first part, estimating a plurality of eigenvectors and eigenvalues of the reduced density matrix, and generating a transformed Hamiltonian matrix. Generating the transformed Hamiltonian matrix may include transforming the single-particle Hamiltonian matrix into a natural-orbital basis of the first part such that the transformed Hamiltonian matrix has a reduced dimensionality. The natural-orbital basis may be spanned by a subset of the eigenvectors of the reduced density matrix.

Abstract: A quantum device includes a syndrome measurement circuit that implements an correction code using a plurality of Majorana qubit islands. The syndrome measurement circuit is adapted to effect a syndrome measurement by performing a sequence of measurement-only operations, where each one of the measurement-only operations involves at most two of the Majorana qubit islands.

Abstract: A computing system is provided, including a processor configured to identify a plurality of measurement sequences that implement a logic gate. Each measurement sequence may include a plurality of measurements of a quantum state of a topological quantum computing device. The processor may be further configured to determine a respective estimated total resource cost of each measurement sequence of the plurality of measurement sequences. The processor may be further configured to determine a first measurement sequence that has a lowest estimated total resource cost of the plurality of measurement sequences. The topological quantum computing device may be configured to implement the logic gate by applying the first measurement sequence to the quantum state.

Abstract: A method for use with a topological quantum computing device is provided. The method may include setting a plurality of device parameters for a qubit architecture including a plurality of Majorana zero modes (MZMs). The method may further include calibrating the plurality of device parameters at least in part by determining whether the plurality of MZMs exhibit ground state degeneracy. When the plurality of MZMs are determined to not exhibit ground state degeneracy, calibrating the plurality of device parameters may further include modifying one or more device parameters of the plurality of device parameters. When the plurality of MZMs are determined to exhibit ground state degeneracy, the method may further include modifying one or more parameters of a measurement device coupled to the qubit architecture.

Abstract: A quantum device includes a syndrome measurement circuit that implements an correction code using a plurality of Majorana qubit islands. The syndrome measurement circuit is adapted to effect a syndrome measurement by performing a sequence of measurement-only operations, where each one of the measurement-only operations involves at most two of the Majorana qubit islands.

Abstract: A computing system is provided, including a processor configured to identify a plurality of measurement sequences that implement a logic gate. Each measurement sequence may include a plurality of measurements of a quantum state of a topological quantum computing device. The processor may be further configured to determine a respective estimated total resource cost of each measurement sequence of the plurality of measurement sequences. The processor may be further configured to determine a first measurement sequence that has a lowest estimated total resource cost of the plurality of measurement sequences. The topological quantum computing device may be configured to implement the logic gate by applying the first measurement sequence to the quantum state.

Abstract: A quantum annealer simulator approximates unitary quantum dynamics of a quantum annealer on a non-quantum computing device such as a conventional computing device. The quantum annealer simulator may utilize algorithms that may efficiently approximate unitary time evolution of a quantum system, where the quantum system corresponds to a problem for which an optimized solution is sought.

Abstract: A quantum annealer simulator approximates unitary quantum dynamics of a quantum annealer on a non-quantum computing device such as a conventional computing device. The quantum annealer simulator may utilize algorithms that may efficiently approximate unitary time evolution of a quantum system, where the quantum system corresponds to a problem for which an optimized solution is sought.