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EP-4742107-A1 - QUANTUM CONVERTER AND QUANTUM CONVERSION METHOD

EP4742107A1EP 4742107 A1EP4742107 A1EP 4742107A1EP-4742107-A1

Abstract

A quantum frequency converter includes a lamina te including at least one topological insulator film and at least one ferromagnetic film that are lamina ted together, and the laminate includes an interface between the topological insulator film and the ferr omagnetic film. The quantum frequency converter incl udes a magnetic field applying unit configured to ap ply a magnetic field with a component perpendicular to the interface to the laminate, and a microwave tr ansceiver configured to transmit and receive a micro wave to and from the laminate. The interface of the laminate is irradiated with laser light. The quantum frequency converter can be used, for example, in a quantum computer.

Inventors

  • SEKINE, AKIHIKO

Assignees

  • FUJITSU LIMITED

Dates

Publication Date
20260513
Application Date
20230704

Claims (13)

  1. A quantum frequency converter comprising: a laminate including: at least one topological insulator film and at least one ferromagnetic film that are laminated together, and an interface between the topological insulator film and the ferromagnetic film; a magnetic field applying unit configured to apply a magnetic field with a component perpendicular to the interface to the laminate; and a microwave transceiver configured to transmit and receive a microwave to and from the laminate, wherein the interface of the laminate is irradiated with laser light.
  2. The quantum frequency converter according to claim 1, further comprising: a microwave resonator, wherein the laminate is provided in the microwave resonator.
  3. The quantum frequency converter according to claim 2, wherein the microwave resonator includes an inlet through which the laser light is to be emitted from outside.
  4. The quantum frequency converter according to claim 3, wherein the microwave resonator includes an outlet through which the laser light, having passed through the laminate, is to be externally emitted.
  5. The quantum frequency converter according to any one of claims 1 to 4, wherein the ferromagnetic film is a ferromagnetic insulator film.
  6. The quantum frequency converter according to claim 5, wherein the ferromagnetic insulator film includes Y 3 Fe 5 O 12 , Tm 3 Fe 5 O 12 , EuS, Cr 2 Ge 2 Te 6 , or BaFe 12 O 19 .
  7. The quantum frequency converter according to any one of claims 1 to 4, wherein the topological insulator film includes Bi 2 Se 3 or (Bi x Sb 1-x ) 2 Te 3 .
  8. The quantum frequency converter according to any one of claims 1 to 4, wherein a thickness of the topological insulator film is greater than or equal to 5 nm and less than or equal to 100 µm.
  9. The quantum frequency converter according to any one of claims 1 to 4, wherein a thickness of the ferromagnetic film is greater than or equal to 1 nm and less than or equal to 30 nm.
  10. The quantum frequency converter according to any one of claims 1 to 4, wherein in the laminate, the at least one topological insulator film includes a plurality of topological insulator films, and the at least one ferromagnetic film includes a plurality of ferromagnetic films.
  11. The quantum frequency converter according to any one of claims 1 to 4, wherein the at least one topological insulator film includes a plurality of topological insulator films, and wherein the laminate includes a nonmagnetic spacer between two adjacent topological insulator films in a lamination direction, among the plurality of topological insulator films.
  12. The quantum frequency converter according to claim 10, wherein a distance between two adjacent topological insulator films in a lamination direction, among the plurality of topological insulator films, is 5 nm or greater.
  13. A quantum frequency conversion method executed by a quantum frequency converter including a laminate including: at least one topological insulator film and at least one ferromagnetic film that are laminated together, and an interface between the topological insulator film and the ferromagnetic film, a magnetic field applying unit configured to apply a magnetic field with a component perpendicular to the interface to the laminate, and a microwave transceiver configured to transmit and receive a microwave to and from the laminate, the quantum frequency conversion method comprising: irradiating the interface of the laminate with laser light.

Description

TECHNICAL FIELD The present disclosure relates to a quantum frequency converter and a quantum frequency conversion method. BACKGROUND In quantum computers, quantum frequency conversion between microwave photons and optical photons is performed in some cases. Quantum frequency converters for quantum frequency conversion have been proposed. RELATED-ART DOCUMENTS PATENT DOCUMENTS Patent Document 1: Japanese National Publication of International Patent Application No. 2013-500530Patent Document 2: Japanese National Publication of International Patent Application No. 2019-512104,Patent Document 3: U.S. Patent Application Publication No. 2022/0215281, Non-PATENT DOCUMENTS Non-Patent Document 1: R. Hisatomi et al., Phys. Rev. B 93, 174427 (2016)Non-Patent Document 2: Tse & MacDonald, Phys. Rev. Lett. 105 057401 (2010)Non-Patent Document 3: J. Maciejko et al., Phys. Rev. Lett. 105 166803 (2010) SUMMARY PROBLEM TO BE SOLVED BY THE INVENTION Conventional quantum frequency converters have low conversion efficiency in quantum frequency conversion. An object of the present disclosure is to provide a quantum frequency converter and a quantum frequency conversion method capable of improving conversion efficiency. MEANS FOR SOLVING THE PROBLEM According to one aspect of the embodiments, a quantum frequency converter includes a laminate including at least one topological insulator film and at least one ferromagnetic film that are laminated together, and including an interface between the topological insulator film and the ferromagnetic film; a magnetic field applying unit configured to apply a magnetic field with a component perpendicular to the interface to the laminate; and a microwave transceiver configured to transmit and receive a microwave to and from the laminate. The interface of the laminate is irradiated with laser ligh. EFFECTS OF THE INVENTION In the present disclosure, conversion efficiency can be improved. BRIEF DESCRIPTION OF DRAWINGS [FIG. 1] FIG. 1 is a schematic diagram illustrating a quantum frequency converter in a first reference example;[FIG. 2] FIG. 2 is a schematic diagram illustrating the quantum frequency converter in a second reference example;[FIG. 3] FIG. 3 is a schematic diagram illustrating the quantum frequency converter according to a first embodiment;[FIG. 4] FIG. 4 is a schematic diagram illustrating the quantum frequency converter according to a second embodiment;[FIG. 5] FIG. 5 is a diagram illustrating the relationship between a thickness of a ferromagnetic film, the number of topological insulator films, and a ratio for conversion efficiency;[FIG. 6] FIG. 6 is a schematic diagram illustrating the quantum frequency converter according to a third embodiment; and[FIG. 7] FIG. 7 is a schematic diagram illustrating the quantum frequency converter according to a fourth embodiment. MODE FOR CARRYING OUT THE INVENTION Hereinafter, embodiments of the present disclosure will be described with reference to the accompanying drawings. In the specification and the drawings, components having substantially the same functional configuration are denoted by the same reference numerals, and redundant description may be omitted. (Reference Examples) First, a first reference example will be described. FIG. 1 is a schematic diagram illustrating a quantum frequency converter in the first reference example. As illustrated in FIG. 1, a quantum frequency converter 100X in the first reference example has a microwave resonator 30, a laminate 10X, an S pole 51, an N pole 52, and an antenna 40. The laminate 10X has a ferromagnetic topological insulator film 11X and a first film 12X. The ferromagnetic topological insulator film 11X has a first surface 11XA and a second surface 11XB opposite to the first surface 11XA. The first film 12X is in contact with the first surface 11XA. The first film 12X is composed of, for example, a nonmagnetic insulator. The first film 12X is a substrate including, for example, SrTiO3, InP, Al2O3, or any combination thereof. The ferromagnetic topological insulator film 11X includes a topological insulator and a ferromagnet with which the topological insulator is doped. For example, the topological insulator includes Bi, Sb, and Te, and the ferromagnet includes Cr or V, or both of Cr and V. The composition of the ferromagnetic topological insulator film 11X is, for example, Crx (Bi1-ySby)2-xTe3 or Vx(Bi1-ySby)2-xTe3. For example, the value of x is greater than or equal to 0.1 and less than or equal to 0.6, and the value of y is greater than or equal to 0.7 and less than or equal to 0.9. The thickness of the ferromagnetic topological insulator film 11X is, for example, greater than or equal to 5 nm and less than or equal to 100 µm. The ferromagnetic topological insulator film 11X has a square planar shape having a side length of about 1 mm in a plan view in a direction perpendicular to the first surface 11XA. The planar shape of the ferromagnetic topological insulator film 11X is not limit