Quantum circuit
AssigneeNEC Corporation
InventorAkihisa Tomita
Life of this patent
Estimating the term…
Abstract
With the object of providing a practical quantum circuit capable of discriminating Bell states in order to realize transmission of quantum states with high fidelity, a quantum circuit comprises: a two-photon absorbing crystal that selectively absorbs, in accordance with known selection rules, a photon pair of a Bell state that is determined depending on crystal symmetry of said two-photon absorbing crystal; a two-photon absorption detector that detects absorption of photon pairs by said two-photon absorbing crystal; and a polarization element that converts the Bell state of a polarized photon pair. The two-photon absorbing crystal makes two-photon absorption of a photon pair of a specific Bell state only. Electrons that have been excited by the two-photon absorption are detected by the detector.
Claims15
A quantum circuit for detecting a quantum state of an optical signal, wherein said quantum state is a Bell state of a polarized photon pair, the directions of polarization of two photons that make up said polarized photon pair being in a fixed relation to each other, and wherein said Bell state of a photon pair is a superposition of the states of said photon pair, each of said states of said photon pair being designated with reference to a set of directions of polarization of individual photons, said quantum circuit comprising:
- a two-photon absorbing crystal having the crystal symmetry selected so that the two-photon absorbing crystal selectively absorbs a photon pair of a prescribed Bell state in accordance with selection rules based on crystal symmetry;
- and
- a two-photon absorption detector that detects absorption of photon pairs by said two-photon absorbing crystal.
A quantum circuit that discriminates Bell states Φ(+) and Φ(−) from polarized photon pairs entangled to four Bell states Φ(+), Φ(−), Ψ(+), and Ψ(−) by using crystals that selectively absorb only a polarized photon pair of a Bell state Ψ(+);
- comprising:
- an optical rotator that rotates the direction of polarization of one of the incident polarized optical signals 90°;
- a first two-photon absorbing crystal that receives the output of said optical rotator and the other of said incident polarized optical signals, and selectively absorbs a polarized photon pair in Bell state Ψ(+) only;
- a first two-photon absorption detector that detects the absorption of photon pairs by said first two-photon absorbing crystal;
- a retarder means that provides a 90° phase difference between the oscillations in polarization directions of one of the photons of said photon pair that have been transmitted by said first two-photon absorbing crystal and provides a −90° phase difference between the oscillations in polarization directions of the other photon of said photon pair;
- a second two-photon absorbing crystal that receives the output of said retarder means, and selectively absorbs a polarized photon pair of Bell state Ψ(+) only;
- and
- a second two-photon absorption detector that detects the absorption of photons pairs by said second two-photon absorbing crystal;
- wherein Φ(+) is a state in which the directions of polarization of the polarized photon pair are the same and that is symmetrical with respect to the exchange of the directions of polarization;
- Φ(−) is a state in which the directions of polarization of a polarized photon pair are the same and that is antisymmetrical with respect to the exchange of the directions of polarization;
- Ψ(+) is a state in which the directions of polarization of a polarized photon pair are orthogonal and that is symmetrical with respect to the exchange of the directions of polarization;
- and Ψ(−) is a state in which the directions of polarization of a polarized photon pair are orthogonal and that is antisymmetrical with respect to the exchange of the directions of polarization.
A quantum circuit for discriminating specific Bell states from polarized optical signal in an entangled state of four Bell states, each Bell state representing a quantum state of a polarized photon pair, said quantum circuit comprising:
- a first two-photon absorbing crystal having the crystal symmetry that permits to absorb a polarized photon pair in either of two Bell states in accordance with selection rules based on crystal symmetry;
- a first power supply that supplies voltage to said first two-photon absorbing crystal such that said first two-photon absorbing crystal selectively absorbs a polarized photon pair in a first Bell state of said two Bell states only;
- a first two-photon absorption detector that detects the absorption of a polarized photon pair by said first two-photon absorbing crystal;
- a second two-photon absorbing crystal having the same crystal structure as said first two-photon absorbing crystal;
- a second power supply that supplies a voltage to said second two-photon absorbing crystal such that said second two-photon absorbing crystal selectively absorbs a polarized photon pair in a second Bell state of said two Bell states only;
- and
- a second two-photon absorption detector that detects the absorption of photon pairs by said second two-photon absorbing crystal.
Dependencies are inferred from the claim text.