Abstract: According to one embodiment, an information processing device includes a qubit pair structure body including a plurality of qubit pairs. The qubit pairs are arranged in m rows and n columns. The qubit pairs include first, and second qubit pairs, and first to sixth adjacent qubit pairs. The qubit pair structure body includes first to eighth spin chains. The first and fifth spin chains include a first eigenenergy, and not include the second, third, and fourth eigenenergies. The second and sixth spin chains include a second eigenenergy, and not include the first, third, and fourth eigenenergies. The third and seventh spin chains include a third eigenenergy, and not include the first, second, and fourth eigenenergies. The fourth spin chain and the eighth spin chain include a fourth eigenenergy, not include the first, second, and third eigenenergies. The first to fourth eigenenergies are different from each other.

Abstract: According to one embodiment, an information processing device includes a qubit pair structure body including a plurality of qubit pairs. The qubit pairs are arranged in m rows and n columns. The qubit pairs include first, and second qubit pairs, and first to sixth adjacent qubit pairs. The qubit pair structure body includes first to eighth spin chains. The first and fifth spin chains include a first eigenenergy, and not include the second, third, and fourth eigenenergies. The second and sixth spin chains include a second eigenenergy, and not include the first, third, and fourth eigenenergies. The third and seventh spin chains include a third eigenenergy, and not include the first, second, and fourth eigenenergies. The fourth spin chain and the eighth spin chain include a fourth eigenenergy, not include the first, second, and third eigenenergies. The first to fourth eigenenergies are different from each other.

Abstract: According to one embodiment, an optical device includes a first mirror, a second mirror, and a first member. The first mirror has a first planar surface. The second mirror is spaced from the first mirror in a first direction crossing the first planar surface. The second mirror has a concave surface including a first region and a second region around the first region. First distance between the first region and the first planar surface in the first direction is longer than second distance between the second region and the first planar surface in the first direction. The first distance is half or less of curvature radius of the concave surface. The first member is light transmissive and solid. The first member includes a first portion provided between the first mirror and the second mirror. The first portion is in contact with the first planar surface and the concave surface.

Abstract: According to one embodiment, a cavity with a cavity mode which is coupled to physical systems includes a spherical mirror and a plane mirror. The spherical mirror is provided at a birefringent crystal including the physical systems. The plane mirror is provided at the birefringent crystal opposite to the spherical mirror. The birefringent crystal has a first refractive index to light polarized in a first direction parallel to a polarization direction of the cavity mode on an optical axis of the cavity and a second refractive index to light polarized in a second direction parallel to the optical axis, the second refractive index being different from the first refractive index. A cavity length of the cavity and a mode waist radius of the cavity mode satisfy a specific condition.

Abstract: According to one embodiment, an optical device includes a first mirror, a second mirror, and a first member. The first mirror has a first planar surface. The second mirror is spaced from the first mirror in a first direction crossing the first planar surface. The second mirror has a concave surface including a first region and a second region around the first region. First distance between the first region and the first planar surface in the first direction is longer than second distance between the second region and the first planar surface in the first direction. The first distance is half or less of curvature radius of the concave surface. The first member is light transmissive and solid. The first member includes a first portion provided between the first mirror and the second mirror. The first portion is in contact with the first planar surface and the concave surface.

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 optical device includes a first mirror, a second mirror, and a first member. The first mirror has a first planar surface. The second mirror is spaced from the first mirror in a first direction crossing the first planar surface. The second mirror has a concave surface including a first region and a second region around the first region. First distance between the first region and the first planar surface in the first direction is longer than second distance between the second region and the first planar surface in the first direction. The first distance is half or less of curvature radius of the concave surface. The first member is light transmissive and solid. The first member includes a first portion provided between the first mirror and the second mirror. The first portion is in contact with the first planar surface and the concave surface.

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, a cavity with a cavity mode which is coupled to physical systems includes a spherical mirror and a plane mirror. The spherical mirror is provided at a birefringent crystal including the physical systems. The plane mirror is provided at the birefringent crystal opposite to the spherical mirror. The birefringent crystal has a first refractive index to light polarized in a first direction parallel to a polarization direction of the cavity mode on an optical axis of the cavity and a second refractive index to light polarized in a second direction parallel to the optical axis, the second refractive index being different from the first refractive index. A cavity length of the cavity and a mode waist radius of the cavity mode satisfy a specific condition.

Abstract: According to one embodiment, a cavity with a cavity mode which is coupled to physical systems includes a spherical mirror and a plane mirror. The spherical mirror is provided at a birefringent crystal including the physical systems. The plane mirror is provided at the birefringent crystal opposite to the spherical mirror. The birefringent crystal has a first refractive index to light polarized in a first direction parallel to a polarization direction of the cavity mode on an optical axis of the cavity and a second refractive index to light polarized in a second direction parallel to the optical axis, the second refractive index being different from the first refractive index. A cavity length of the cavity and a mode waist radius of the cavity mode satisfy a specific condition.

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 cavity with a cavity mode which is coupled to physical systems includes a spherical mirror and a plane mirror. The spherical mirror is provided at a birefringent crystal including the physical systems. The plane mirror is provided at the birefringent crystal opposite to the spherical mirror. The birefringent crystal has a first refractive index to light polarized in a first direction parallel to a polarization direction of the cavity mode on an optical axis of the cavity and a second refractive index to light polarized in a second direction parallel to the optical axis, the second refractive index being different from the first refractive index. A cavity length of the cavity and a mode waist radius of the cavity mode satisfy a specific condition.

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 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.