QUANTUM COMPUTER AND QUANTUM COMPUTING METHOD

• US 20160321558A1
• Filed: 07/15/2016
• Published: 11/03/2016
• Est. Priority Date: 01/16/2014
• Status: Active Grant

• Current Assignee: Kabushiki Kaisha Toshiba (Toshiba Corporation)
• Original Assignee: Kabushiki Kaisha Toshiba (Toshiba Corporation)
• Inventors: ICHIMURA, Kouichi, KUJIRAOKA, Mamiko, NAKAMURA, Satoshi, GOTO, Hayato
• Granted Patent: US 10,068,182 B2
• Time in Patent Office: Days
• US Class Current: 1/1
• CPC Class Codes: G02F 1/0126 Opto-optical modulation, i.e. control of one light beam by another light beam, not otherwise provided for in this subclass
• CPC Class Codes: G02F 2203/05 wavelength dependent
• CPC Class Codes: G02F 2203/15 involving resonance effects, e.g. resonantly enhanced interaction
• CPC Class Codes: G02F 3/00 Optical logic elements; Optical bistable devices
• CPC Class Codes: G06N 10/00 Quantum computing, i.e. information processing based on quantum-mechanical phenomena
• CPC Class Codes: H01S 3/00 Lasers, i.e. devices using stimulated emission of electromagnetic radiation in the infrared, visible or ultraviolet wave range semiconductors lasers H01S5/00

Abstract

According to an embodiment, a quantum computer includes physical systems X_i, a physical system Y_j and a light source unit. The physical systems X_i and the physical system Y_j are provided in a cavity. Each physical system X_i 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 Y_j 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 X_i, the laser beams including a laser beam for collecting population in the state |2>′_j in the |2>′_j-|e>′_j transition.

Claims

1. A quantum computer comprising:

physical systems X_i (i=1, 2, . . . , N;

N being an integer not less than

     2) provided in a cavity, each of the physical systems X_i comprising at least four states including states |0>

_i, |1>

_i, |2>

_i and |e>

_i, energy of the state |e>

_i being higher than energy of the states |0>

_i and |1>

i used for a qubit and energy of the state |2>

_i used for assisting a gate operation, a |2>

_i-|e>

_i transition being resonant with a cavity mode of the cavity;

a physical system Y_j (j=1, 2, . . . , N₂;

N₂ being an integer not less than

     1) provided in the cavity, the physical system Y_j being different from the physical systems X_i, the physical system Y_j comprising at least two energy states including states |2>

′

_j and |e>

′

_j, energy of the state |e>

′

_j being higher than energy of the state |2>

′

_j, a |2>

′

_j−

|e>

′

_j transition being resonant with the cavity mode; and

a light source unit which applies laser beams to the cavity to manipulate a state of a physical system X_s (where s is a natural number not more than N) and a state of physical system X_t (where t is a natural number not more than N and different from s) of the physical systems X_i, the laser beams including a first laser beam resonating with a |1>

_s-|e>

_s transition, a second laser beam resonating with a |1>

_t-|e>

_t transition, and a third laser beam for collecting population in the state |2>

′

_j in the |2>

′

_j-|e>

′

_j transition of the physical system Y_j.

2. The quantum computer according to claim 1, wherein the light source unit comprises:

a light source which emits a laser beam;

two beam splitters which divide the laser beam into a first branch laser beam, a second branch laser beam and a third branch laser beam;

a first optical modulator which modulates the first branch laser beam to generate the first laser beam;

a second optical modulator which modulates the second branch laser beam to generate the second laser beam; and

a third optical modulator which modulates the third branch laser beam to generate the third laser beam.

3. The quantum computer according to claim 1, wherein the light source unit comprises:

a first light source;

a first optical modulator which modulates a laser beam emitted from the first light source to generate the first laser beam;

a second light source;

a second optical modulator which modulates a laser beam emitted from the second light source to generate the second laser beam;

a third light source; and

a third optical modulator which modulates a laser beam emitted from the third light source to generate the third laser beam.

4. The quantum computer according to claim 1, wherein the cavity comprises a first space region including the physical systems X_i, and a second space region including the physical system Y_i, the second space region being different from the first space region, and the light source unit applies the third laser beam to the second space region.

5. A quantum computing method comprising:

preparing physical systems X_i (i=1, 2, . . . , N;

N being an integer not less than

     2) provided in a cavity, each of the physical systems X_i comprising at least four states including states |0>

_i, |1>

_i, |2>

_i and |e>

_i, energy of the state |e>

_i is higher than energy of the states |0>

_i and |1>

i used for a qubit and energy of the state |2>

_i used for assisting a gate operation, a |2>

_i-|e>

_i transition being resonant with a cavity mode of the cavity;

preparing a physical system Y_j (j=1, 2, . . . , N₂;

N₂ being an integer not less than

     1) provided in the cavity, the physical system Y_j being different from the physical systems X_i, physical system Y_j comprising at least two energy states including |2>

′

_j and |e>

′

_j, energy of the state |e>

′

_j being higher than energy of the state |2>

′

_j, a |2>

′

_j-|e>

t_j transition being resonant with the cavity mode; and

applying laser beams to the cavity to manipulate state of a physical system X, (where s is a natural number not more than N) and a state of physical system X_t (where t is a natural number not more than N and different from s) of the physical systems X_i, the laser beams including a first laser beam resonating with a |1>

_s-|e>

_s transition, a second laser beam resonating with a |1>

_t-|e>

_t transition, and a third laser beam for collecting population in the state |2>

′

_j in the |2>

′

_j-|e>

transition of the physical system Y.

6. The quantum computing method according to claim 5, further comprising:

applying the first laser beam and the second laser beam to the cavity, after applying the third laser beam to collect population in the state |2>

′

_j of the physical system Y_j.

7. The quantum computing method according to claim 5, wherein if the physical systems X, comprises physical systems X_i, X₂, . . . , X_N in ascending order of frequency of a |1>

_i-|e>

, transition, a frequency difference between a |1>

_i-|e>

₁ transition and a |1>

₂-|e>

₂ transition is Δ

, and a frequency difference between a |1>

₁-|e>

₁ transition and a |1>

_k-|e>

_k transition is L_k, then the plurality of physical systems X_i satisfy;

Ω

₀<

Δ

<

N₂g/N and Ω

₀<

Δ

_k<

N₂g/N,

where g is a coupling constant between the cavity mode and each of the physical systems X_i, and Ω

₀ is a parameter for determining a maximum value of Rabi frequencies of the first laser beam and the second laser beam.

8. The quantum computing method according to claim 5, wherein N₂≧

N² is satisfied.