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: A quantum bit computation method includes operating a two-quantum-bit gate on quantum bits of a first physical system and a second physical system, second energy states of second physical systems except for the first physical system and the second physical system do not change, three energy states being represented by |0>, |1> and |3>, the two energy states being represented by |2> and |4>, energies of |2> and |4> being higher than energies of |0>, |1> and |3>, a transition frequency between |3> and |2> being equal to the resonance frequency, |0> and |1> representing quantum bits, flipping quantum bits of first physical systems after operating the two-quantum-bit gate, executing no operations by a time equal to a time for operating the two-quantum-bit gate, after flipping the quantum bits, and again flipping the quantum bits of the first physical systems after executing no operations.

Abstract: An optical resonator includes a master resonator configured to resonate an electromagnetic wave, one structure or a pair of structures adjacent to each other, each of which is arranged at a position that overlaps one of resonance modes of the master resonator, is made up of a material in which a real part of a permittivity assumes a negative value, and an absolute value of the real part is larger than an absolute value of an imaginary part of the permittivity, and has a size which makes scattering that the electromagnetic wave suffers be Rayleigh scattering, and one or a plurality of particles, each of which is laid out near the structure by a distance smaller than the size of the structure.

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: 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: A method includes causing a common-resonator mode resonating with a transition between |2>i and |3>i that are coupled to each other by a transition having a homogenous broadening ?Ehomo greater than an energy difference between |0>i and |1>i, an energy difference between |2>i and |3>i being greater than ?Ehomo, transferring states of m quantum bits represented by |0>k and |1>k to |4>k and |5>k, respectively, when a quantum-bit-gate operation using the common-resonator mode is executed between the quantum bits represented by m physical systems k, |E(|u>k)?E(|v>k)|>?Ehomo, u, v?{2, 3, 4, 5}, u?v, executing adiabatic passage between the physical systems k, using light that resonates with a transition between |3>k and |4>k and a transition between |3>k and |5>k, executing the quantum-bit-gate operation between the quantum bits, and transferring, to |0>k and |1>k, the states represented by |4>k and |5>k, respectively.

Abstract: A quantum bit computation method includes operating a two-quantum-bit gate on quantum bits of a first physical system and a second physical system, second energy states of second physical systems except for the first physical system and the second physical system do not change, three energy states being represented by |0>, |1> and |3>, the two energy states being represented by |2> and |4>, energies of |2> and |4> being higher than energies of |0>, |1> and |3>, a transition frequency between |3> and |2> being equal to the resonance frequency, |0> and |1> representing quantum bits, flipping quantum bits of first physical systems after operating the two-quantum-bit gate, executing no operations by a time equal to a time for operating the two-quantum-bit gate, after flipping the quantum bits, and again flipping the quantum bits of the first physical systems after executing no operations.

Abstract: In a cavity mode of a cavity, a diameter of a mode waist is decreased so that the diameter is similar to a wavelength of an electromagnetic wave resonant with the cavity mode, when a material is located in the cavity. The material includes a physical system having two quantum states. A relative position between the material and the mode waist is scanned along three-directions unparallel mutually. A laser coupled with the cavity mode is input to the cavity. An intensity of at least one of a reflected light and a transmitted light of the laser from the cavity is measured.

Abstract: A quantum computer includes a unit including thin films A, B and C each containing a physical-system group A, B and C formed of physical systems A, B and C, the films A, B and C being alternately stacked in an order of A, B, C, A, . . . , each of the systems A, B and C having three-different-energy states |0>x, |1>x , |e>x, a quantum bit being expressed by a quantum-mechanical-superposition state of |0>x and |1>x , a light source generating light beams having angular frequencies ?A(E), ye, g, ?A(E), ye, e, ?x, ye, gg, ?x, ye, ge, ?x, ye, eg and ?x, ye, ee, ?A(E), ye, g, a unit controlling frequencies and intensities of the beams, and a unit measuring intensity of light emitted from or transmitted through physical-system group A(E) contained in a lowest one of the thin films A to detect a quantum state of the group A(E).

Abstract: A quantum bit computation method includes operating a two-quantum-bit gate on quantum bits of a first physical system and a second physical system, second energy states of second physical systems except for the first physical system and the second physical system do not change, three energy states being represented by |0>, |1> and |3>, the two energy states being represented by |2> and |4>, energies of |2> and |4> being higher than energies of |0>, |1> and |3>, a transition frequency between |3> and |2> being equal to the resonance frequency, |0> and |1> representing quantum bits, flipping quantum bits of first physical systems after operating the two-quantum-bit gate, executing no operations by a time equal to a time for operating the two-quantum-bit gate, after flipping the quantum bits, and again flipping the quantum bits of the first physical systems after executing no operations.

Abstract: An (N+1) number of physical systems each having five energy levels |0>, |1>, |2>, |3>, and |4>, a qubit being expressed by |0> and |1>, are provided in an optical cavity having a cavity mode resonant with |2>-|3>, such that an N number of control systems and a target system are prepared. The target system is irradiated with light pulses resonant with |0>-|4>, |1>-|4>, and |2>-|4> to change a superposed state |c> to |2>. All of the physical systems are irradiated with light pulses resonant with |0>-|3> and |1>-|3>, and a phase of the light pulse resonant with the target system is shifted by a specific value dependent on a unitary transformation U. The target system is irradiated with light pulses resonant with |0>-|4>, |1>-|4>, and |2>-|4>, with a phase difference between them being set to a specific value dependent on the unitary transformation U, to return |2> to |c>.

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.

Abstract: A method of generating a single photon, includes preparing an optical resonator including a resonator mode of a resonance angular frequency ?c, preparing a material contained in the optical resonator, including a low energy state |g> and a high energy state |e>, and including a transition angular frequency ?a between |g>?|e> that is varied by an external field, applying, to the material, light of an angular frequency ?l different from the resonance angular frequency ?c, and applying a first external field to the material to vary the transition angular frequency ?a to resonate with the angular frequency ?l, such that a state of the material is changed to |e>, and then applying a second external field to the material to vary the transition angular frequency ?a to resonate with the resonance angular frequency ?c, such that the state of the material is restored to |g>.

Abstract: Quantum information processing device includes resonator incorporating material containing physical systems, each of physical systems having at least four energy states, transition between two energy states of at least four energy states, and transition energy between at least two energy states of at least four energy states, at least four energy states being non-degenerate when magnetic field fails to be applied to physical systems, transition resonating in resonator mode that is in common between physical systems, each of at least four energy states representing a quantum bit, transition energy being shifted when magnetic field is applied to physical systems, and magnetic-field application unit configured to apply magnetic field having direction and intensity to material, to eliminate linear transition energy shift between two energy states included in physical systems, each of two energy states included in physical systems being with excluding two energy states resonating in resonator mode.

Abstract: In a cavity mode of a cavity, a diameter of a mode waist is decreased so that the diameter is similar to a wavelength of an electromagnetic wave resonant with the cavity mode, when a material is located in the cavity. The material includes a physical system having two quantum states. A relative position between the material and the mode waist is scanned along three-directions unparallel mutually. A laser coupled with the cavity mode is input to the cavity. An intensity of at least one of a reflected light and a transmitted light of the laser from the cavity is measured.

Abstract: A method includes causing a common-resonator mode resonating with a transition between |2>i and |3>i that are coupled to each other by a transition having a homogenous broadening ?Ehomo greater than an energy difference between |0>i and |1>i, an energy difference between |2>i and |3>i being greater than ?Ehomo, transferring states of m quantum bits represented by |0>k and |1>k to |4>k and |5>k, respectively, when a quantum-bit-gate operation using the common-resonator mode is executed between the quantum bits represented by m physical systems k, |E(|u>k)?E(|v>k)|>?Ehomo, u, v?{2, 3, 4, 5}, u?v, executing adiabatic passage between the physical systems k, using light that resonates with a transition between |3>k and |4>k and a transition between |3>k and |5>k, executing the quantum-bit-gate operation between the quantum bits, and transferring, to |0>k and |1>k, the states represented by |4>k and |5>k, respectively.

Abstract: A quantum computer includes a unit including thin films A, B and C each containing a physical-system group A, B and C formed of physical systems A, B and C, the films A, B and C being alternately stacked in an order of A, B, C, A, . . . , each of the systems A, B and C having three-different-energy states |0>X, |1>X, |e>x, a quantum bit being expressed by a quantum-mechanical-superposition state of |0>X and |1>X, a light source generating light beams having angular frequencies ?A(E), ye, g, ?A(E), ye, e, ?x, ye, gg, ?x, ye, ge, ?x, ye, eg and ?x, ye, ee, ?A(E), ye, g, a unit controlling frequencies and intensities of the beams, and a unit measuring intensity of light emitted from or transmitted through physical-system group A(E) contained in a lowest one of the thin films A to detect a quantum state of the group A(E).

Abstract: An apparatus includes a material in a resonator and containing systems, each of the systems having five energy states, a unit generating first and second pulse that resonate in a second transition and a third transition, respectively, a unit controlling the first and second pulse to make the first and second pulse temporally overlap each other to obtain third light, a unit emitting the third light to each system, a unit generating observation light to be coupled to the resonator mode, a unit introducing the observation light to the resonator from an outside thereof, a unit reading one of quantum bits by measuring an intensity of one of reflected light and transmitted light of the observation light, a unit controlling the first and second pulse to make the first and second pulse temporally overlap each other to obtain fourth light, and a unit emitting the fourth light to each system.

Abstract: A quantum bit computation method includes operating a two-quantum-bit gate on quantum bits of a first physical system and a second physical system, second energy states of second physical systems except for the first physical system and the second physical system do not change, three energy states being represented by |0>, |1> and |3>, the two energy states being represented by |2> and |4>, energies of |2> and |4> being higher than energies of |0>, |1> and |3>, a transition frequency between |3> and |2> being equal to the resonance frequency, |0> and |1> representing quantum bits, flipping quantum bits of first physical systems after operating the two-quantum-bit gate, executing no operations by a time equal to a time for operating the two-quantum-bit gate, after flipping the quantum bits, and again flipping the quantum bits of the first physical systems after executing no operations.

Abstract: An optical resonator includes a master resonator configured to resonate an electromagnetic wave, one structure or a pair of structures adjacent to each other, each of which is arranged at a position that overlaps one of resonance modes of the master resonator, is made up of a material in which a real part of a permittivity assumes a negative value, and an absolute value of the real part is larger than an absolute value of an imaginary part of the permittivity, and has a size which makes scattering that the electromagnetic wave suffers be Rayleigh scattering, and one or a plurality of particles, each of which is laid out near the structure by a distance smaller than the size of the structure.