Abstract: According to an embodiment, a quantum computer includes physical systems Xi, a physical system Yj and a light source unit. The physical systems Xi and the physical system Yj are provided in a cavity. Each physical system Xi includes states |0>i, |1>i, |2>i and |e>i, the states |0>i and |1>i being used for a qubit, a |2>i-|e>i transition being resonant with a cavity mode of the cavity. The physical system Yj includes states |2>?j and |e>?j, a |2>?j-|e>?j transition being resonant with the cavity mode. The light source unit applies laser beams to the cavity to manipulate states of two of physical systems Xi, the laser beams including a laser beam for collecting population in the state |2>?j in the |2>?j-|e>?j transition.

Abstract: According to an embodiment, a computing apparatus includes spin torque oscillators, an interaction unit, a variable direct-current supply device, and a measuring unit. The interaction unit controls an interaction between the spin torque oscillators. The variable direct-current supply device supplies a current to induce oscillations of the spin torque oscillators. The measuring unit measures AC signals obtained from the spin torque oscillators.

Abstract: According to one embodiment, an acousto-optic modulator includes an acousto-optic medium and a piezoelectric transducer. The acousto-optic medium has a configuration of a hexahedron. The acousto-optic medium has surfaces D, E, F, G and H. The piezoelectric transducer is provided on a surface C of the acousto-optic medium. The surface D opposes the surface C and has respective four sides shared by the surfaces E, F, G and H. Four angles defined between the surface D and the surfaces E, F G and H each is other than 90°. At least one of eight angles defined between each pair of the surfaces C, E, F, G and H is other than 90°. The each pair has one shared side.

Abstract: According to one embodiment, a computing device includes a first conductive body, a first element, a second element, a first transmission line and a second transmission line. The first conductive body spreads along a first plane. The first element includes a Josephson junction and is separated from the first conductive body in a direction crossing the first plane. The second element includes a Josephson junction. The second element is separated from the first conductive body in the direction crossing the first plane. A direction from the first element toward the second element is along a first direction along the first plane. The first transmission line generates an electromagnetic field applied to the first element. The second transmission line generates an electromagnetic field applied to the second element.

Abstract: According to one embodiment, a computing device includes an oscillator network and a controller. The oscillator network includes a plurality of oscillators coupled to each other. The controller is configured to control the oscillator network. Each of the oscillators has a nonlinear energy shift. The controller multiply performs a sampling operation. The sampling operation includes a first operation a first operation of outputting a signal causing the oscillators to stop oscillating, a second operation of outputting a signal causing the oscillators to oscillate based on a parameter relating to a first probability distribution, and a third operation of outputting a signal to measure, for the oscillators, a phase of an electromagnetic wave generated by an oscillation.

Abstract: According to one embodiment, an oscillation device includes a resonator, an electromagnetic wave application portion, a filter, and a conductive portion. The resonator includes a Josephson junction. The electromagnetic wave application portion applies a first electromagnetic wave and a second electromagnetic wave to the resonator. The first electromagnetic wave has a component of a first frequency. The second electromagnetic wave has a component of the first frequency and a component of a second frequency. The conductive portion transmits an electromagnetic wave passing through the filter. The resonator oscillates at a third frequency due to the first electromagnetic wave and oscillates at the third frequency and a fourth frequency due to the second electromagnetic wave. A transmittance of the filter for the fourth frequency is higher than a transmittance of the filter for the third frequency.

Abstract: According to an embodiment, a computing apparatus includes spin torque oscillators, an interaction unit, a variable direct-current supply device, and a measuring unit. The interaction unit controls an interaction between the spin torque oscillators. The variable direct-current supply device supplies a current to induce oscillations of the spin torque oscillators. The measuring unit measures AC signals obtained from the spin torque oscillators.

Abstract: According to one embodiment, a quantum computation apparatus includes a plurality of quantum nonlinear oscillators, a controller, and a measuring device. Each of the quantum nonlinear oscillators implements superposition of distinguishable quantum states by bifurcating one quantum state via a quantum adiabatic change controlled by a bifurcation parameter. The quantum nonlinear oscillators couple with each other by nondissipative coupling accompanying no loss. The controller individually controls the bifurcation parameters of the quantum nonlinear oscillators. A measuring device measures outputs from the quantum nonlinear oscillators.

Abstract: According to an embodiment, a quantum computer includes first physical systems provided in a cavity, a second physical system provided in the cavity, and a light source unit. The first physical systems include a transition coupled to a common cavity mode of the cavity. The second physical system includes a first transition coupled to the common cavity mode and a second transition. The light source unit generates a first and a second light beam to manipulate two of the first physical systems and generates a third light beam that resonates with the second transition. The third light beam is radiated to the second physical system during a period when the first and the second light beam are simultaneously radiated to the two first physical systems.

Abstract: According to one embodiment, an acousto-optic modulator includes an acousto-optic medium and a piezoelectric transducer. The acousto-optic medium has a configuration of a hexahedron. The acousto-optic medium has surfaces D, E, F, G and H. The piezoelectric transducer is provided on a surface C of the acousto-optic medium. The surface D opposes the surface C and has respective four sides shared by the surfaces E, F, G and H. Four angles defined between the surface D and the surfaces E, F G and H each is other than 90°. At least one of eight angles defined between each pair of the surfaces C, E, F, G and H is other than 90°. The each pair has one shared side.

Abstract: According to an embodiment, a quantum computer includes physical systems Xi, a physical system Yj and a light source unit. The physical systems Xi and the physical system Yj are provided in a cavity. Each physical system Xi includes states |0>i, |1>i, |2>i and |e>i, the states |0>i and |1>i being used for a qubit, a |2>i-|e>i transition being resonant with a cavity mode of the cavity. The physical system Yj includes states |2>?j and |e>?j, a |2>?j-|e>?j transition being resonant with the cavity mode. The light source unit applies laser beams to the cavity to manipulate states of two of physical systems Xi, the laser beams including a laser beam for collecting population in the state |2>?j in the |2>?j-|e>?j transition.

Abstract: According to one embodiment, an acousto-optic modulator includes an acousto-optic medium and a piezoelectric transducer. The acousto-optic medium has a configuration of a hexahedron. The acousto-optic medium has surfaces D, E, F, G and H. The piezoelectric transducer is provided on a surface C of the acousto-optic medium. The surface D opposes the surface C and has respective four sides shared by the surfaces E, F, G and H. Four angles defined between the surface D and the surfaces E, F, G and H each is other than 90°. At least one of eight angles defined between each pair of the surfaces C, E, F, G and H is other than 90°. The each pair has one shared side.

Abstract: According to one embodiment, a magic state generation apparatus includes first encoder, state distiller, second encoder, and error detector. The first encoder encodes a magic state of a physical quantum bit into a level-1 encoded magic state. The state distiller receives n level-L encoded magic states, performs error detection when reading a level-L encoded quantum bit, performs post-selection which accepts the encoded quantum bit only when no error is detected, and outputs k level-L encoded magic states each having a low error probability (1?L?M?1, and k<n). The second encoder encodes a level-L into a level-(L+1) encoded magic states. The error detector performs error detection on the level-(L+1) encoded magic state, and obtains a level-(L+1) encoded magic state from which an error is removed.

Abstract: According to one embodiment, a quantum computer includes a crystal, an optical resonator, and a light source. A host crystal included in the crystal satisfying three conditions a first condition that maximum phonon energy of the host crystal is low, and so that a homogenous broadening of a 3F3(1) level of the Pr3+ ion resulting from relaxation due to phonon emission is smaller than respective hyperfine splits of a 3H4(1) level and the 3F3(1) level of the Pr3+ ion, a second condition that a site of the Pr3+ ion does not have inversion symmetry, and the Pr3+ ion has a Stark level in which the 3H4(1) level and the 3F3(1) level of the Pr3+ ion are not degenerate, and a third condition that each atom in the host crystal has no electronic magnetic moment.

Abstract: According to one embodiment, a decoding apparatus includes first and second acquisition units, a holding unit, a calculation unit, and a decision unit. The first acquisition unit acquires first measurement values of measurements performed to measure an eigenvalue of an encoded Z operator to a first encoded qubit of the two encoded qubits. The second acquisition unit acquires second measurement values of measurements performed to measure an eigenvalue of an encoded X operator to a second encoded qubit of the two encoded qubits. The holding unit holds error probabilities for the first measurement values and the second measurement values. The calculation unit calculates probabilities for measurement values of an encoded Bell measurement by using the first measurement values, the second measurement values, and the error probabilities. The decision unit decides measurement values of the encoded Bell measurement, based on the calculated probabilities.

Abstract: According to one embodiment, a mirror includes a plurality of dielectric layers stacked in a first direction. A thickness along the first direction of each of the dielectric layers is half a design wavelength. The dielectric layers include a first dielectric layer. The first dielectric layer includes a first portion with a thickness being ? of the design wavelength, a second portion stacked with the first portion with a thickness being ? of the design wavelength, and a third portion provided between the first and second portions with a thickness being ¼ of the design wavelength. The second portion has a refractive index lower than that of the first portion. The third portion has a refractive index gradually decreasing from a side of the first portion toward a side of the second portion.

Abstract: According to one embodiment, a decoding apparatus includes first and second acquisition units, a holding unit, a calculation unit, and a decision unit. The first acquisition unit acquires first measurement values of measurements performed to measure an eigenvalue of an encoded Z operator to a first encoded qubit of the two encoded qubits. The second acquisition unit acquires second measurement values of measurements performed to measure an eigenvalue of an encoded X operator to a second encoded qubit of the two encoded qubits. The holding unit holds error probabilities for the first measurement values and the second measurement values. The calculation unit calculates probabilities for measurement values of an encoded Bell measurement by using the first measurement values, the second measurement values, and the error probabilities. The decision unit decides measurement values of the encoded Bell measurement, based on the calculated probabilities.

Abstract: An operating method for stimulated Raman adiabatic passage to change probability amplitude in a three-level system including states of |0>, |1> and |e>, includes the following two steps. One is to direct a first laser beam and a second laser beam which have frequencies in the vicinity of resonance frequencies corresponding to energy differences between |0> and |e> and between |1> and |e>, respectively. The other is to change temporally two-photon detuning to be a difference between first detuning and second detuning. The first detuning is a difference between a first energy difference and a frequency of the first laser beam. The first energy difference is a difference between energy of |0> and energy of |e>. The second detuning is a difference between a second energy difference and a frequency of the second laser beam. The second energy difference is a difference between energy of |1> and energy of |e>.

Abstract: According to one embodiment, an acousto-optic modulator includes an acousto-optic medium and a piezoelectric transducer. The acousto-optic medium has a configuration of a hexahedron. The acousto-optic medium has surfaces D, E, F, G and H. The piezoelectric transducer is provided on a surface C of the acousto-optic medium. The surface D opposes the surface C and has respective four sides shared by the surfaces E, F, G and H. Four angles defined between the surface D and the surfaces E, F, G and H each is other than 90°. At least one of eight angles defined between each pair of the surfaces C, E, F, G and H is other than 90°. The each pair has one shared side.

Abstract: In an operation of two qubit gate having failure information related to success or failure, by using a code to concatenate N-error-correcting code transversally executing a Pauli gate, a Hadamard gate and a CNOT gate, an error-correction is executed by an error-correcting teleportation, and the CNOT gate is executed to an encoded qubit by the error-correcting teleportation. In Bell measurement of the error-correcting teleportation, when a measurement result of non-encoded qubit is processed, by suitably defining failure information of the encoded qubit of level (l+1) from the failure information of encoded qubits of level l, the measurement result of the encoded qubit of each level is determined, and the failure information of the encoded qubit of each level is defined. As a result, a measurement result of a logical qubit as the encoded qubit of the highest level is determined.