Quantum computer and quantum computing method

Patent metadata

Field	Value
Publication number	US-10068182-B2
Application number	US-201615211112-A
Country	US
Kind code	B2
Filing date	Jul 15, 2016
Priority date	Jan 16, 2014
Publication date	Sep 4, 2018
Grant date	Sep 4, 2018

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.

First claim

What is claimed is:

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, . . . , N 2 ; N 2 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, . . . , N 2 ; N 2 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>′ j transition being resonant with the cavity mode; and
applying laser beams to the cavity to manipulate 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 .

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 i comprises physical systems X i , X 2 , . . . , X N in ascending order of frequency of a |1> i -|e> i 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 |l> 1 -|e> 1 transition and a |1> k -|e> k transition is Δ k , then the plurality of physical systems X i satisfy:
Ω 0 <Δ<N 2 g/N and Ω 0 <Δ k <N 2 g/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 N 2 ≥N 2 is satisfied.

Assignees

• Toshiba Kk

Inventors

• Nakamura Satoshi
• Ichimura Kouichi
• Goto Hayato
• Kujiraoka Mamiko

Classifications

• H01S3/00

  Lasers, i.e. devices using stimulated emission of electromagnetic radiation in the infrared, visible or ultraviolet wave range (semiconductors lasers H01S5/00) · CPC title

• G02F2203/05

  wavelength dependent · CPC title

• G02F2203/15

  involving resonance effects, e.g. resonantly enhanced interaction · CPC title

• G02F3/00

  Optical logic elements; Optical bistable devices · CPC title

• G02F1/0126

  Opto-optical modulation, i.e. control of one light beam by another light beam, not otherwise provided for in this subclass · CPC title