# US 2020/0287631 A1 · Generation of entangled qubit states

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- Number: US 2020/0287631 A1
- Document ID: US20200287631A1
- Status: Published application
- Kind: A1
- Application number: 16/621,994
- Filed: 2019-03-22
- Published: 2020-09-10
- Earliest claimed: 2018-03-23
- Assignees: Psiquantum, Corp.
- Applicants: Psiquantum Corp.
- Inventors: Mercedes GIMENO-SEGOVIA; Terence G. RUDOLPH
- Web page: https://patentgrep.com/patent/US20200287631A1

## CPC

- H04B 10/70: Photonic quantum communication
- G06N 10/40: Physical realisations or architectures of quantum processors or components for manipulating qubits, e.g. qubit coupling or qubit control
- H04B 10/614: {comprising one or more polarization beam splitters, e.g. polarization multiplexed [PolMux] X-PSK coherent receivers, polarization diversity heterodyne coherent receivers (H04J14/06 takes precedence)}
- G02B 2006/12147: {Coupler}
- G02B 2006/12159: {Interferometer}
- H04B: TRANSMISSION
- G06N: COMPUTING ARRANGEMENTS BASED ON SPECIFIC COMPUTATIONAL MODELS
- G02B: OPTICAL ELEMENTS, SYSTEMS OR APPARATUS

## Abstract

A method includes receiving Bell pairs. Photons are obtained in a Greenberger-Hom-Zeilinger (GHZ) state by providing, to a first beam splitter, a photon from a first Bell pair and a photon from a second Bell pair. The first beam splitter is coupled with a first output channel and a second output channel. Obtaining the photons in the GHZ state further includes providing, to a second beam splitter, a photon from a third Bell pair and a photon from a fourth Bell pair. The second beam splitter is coupled with a third output channel arid a fourth output channel. Obtaining the photons in the GHZ state further includes providing a photon output from the second output channel as a first input to a detector and a photon output in the third output channel a second input to the first detector.

## Claims

### Claim 1

A method, comprising:
receiving a plurality of photon pairs, each photon pair being in a Bell state and including a first photon and a second photon that is distinct and separate from the first photon; and
obtaining a plurality of photons comprising at least six photons in a Greenberger-Horn-Zeilinger (GHZ) state by:
providing photons of the plurality of photon pairs to a plurality of beam splitters, including:
providing a first photon of a first photon pair as a first input to a first beam splitter and a first photon of a second photon pair as a second input to the first beam splitter, wherein the first beam splitter is coupled with a first output channel of the first beam splitter and a second output channel of the first beam splitter; and
providing a first photon of a third photon pair as a first input to a second beam splitter and a first photon of a fourth photon pair as a second input to the second beam splitter that is distinct from the first beam splitter, wherein the second beam splitter is coupled with a first output channel of the second beam splitter and a second output channel of the second beam splitter; and
providing a photon output from the first beam splitter in the second output channel of the first beam splitter as a first input to a first fusion gate and a photon output from the second beam splitter in the first output channel of the second beam splitter as a second input to the first fusion gate.

### Claim 2 (depends on 1)

The method of claim 1, wherein:
only one photon is output from the first beam splitter in the second output channel of the first beam splitter; and
only one photon is output from the second beam splitter in the first output channel of the second beam splitter.

### Claim 3 (depends on 1)

The method of claim 1, wherein the plurality of photons in the GHZ state includes:
second photons of: the first photon pair, the second photon pair, the third photon pair, and the fourth photon pair.

### Claim 4 (depends on 3)

The method of claim 3, wherein:
the plurality of photons in the GHZ state includes:
one photon output from the first beam splitter in the first output channel of the first beam splitter; and
one photon output from the second beam splitter in the second output channel of the second beam splitter.

### Claim 5 (depends on 4)

The method of claim 4, wherein the GHZ state is a 6-photon GHZ state produced using 4 pairs of photons in a Bell state.

### Claim 6 (depends on 1)

The method of claim 1, further including:
detecting, using the first fusion gate, a first state of the photon provided as the first input to the first fusion gate and a second state of the photon provided as the second input to the first fusion gate; and
determining whether the first state and the second state are indicative of a 6-photon GHZ state.

### Claim 7 (depends on 1)

The method of claim 1, wherein:
the first fusion gate includes a first detector and a second detector that is distinct and separate from the first detector; and
the method includes detecting, using the first detector of the first fusion gate, only one photon selected from the photon provided as the first input to the first fusion gate and the photon provided as the second input to the first fusion gate and detecting, using the second detector of the first fusion gate, only another photon selected from the photon provided as the first input to the first fusion gate and the photon provided as the second input to the first fusion gate.

### Claim 8 (depends on 1)

The method of claim 1, further including:
providing a first photon of a fifth photon pair as a first input to a third beam splitter and a first photon of a sixth photon pair as a second input to the third beam splitter that is distinct from the first beam splitter and the second beam splitter, wherein the third beam splitter is coupled with a first output channel of the third beam splitter and a second output channel of the third beam splitter; and
providing a photon output from the second beam splitter in the second output channel of the second beam splitter as a first input to a second fusion gate and a photon output from the third beam splitter in the first output channel of the third beam splitter as a second input to the second fusion gate.

### Claim 9 (depends on 8)

The method of claim 8, wherein:
the plurality of photons in the GHZ state includes:
second photons of: the first photon pair, the second photon pair, the third photon pair, the fourth photon pair, the fifth photon pair, and the sixth photon pair;
one photon output from the first beam splitter in the first output channel of the first beam splitter; and
one photon output from the third beam splitter in the second output channel of the third beam splitter.

### Claim 10 (depends on 9)

The method of claim 9, wherein the GHZ state is an 8-photon GHZ state produced using 6 pairs of photons in a Bell state.

### Claim 11 (depends on 8)

The method of claim 8, further including:
providing a first photon of a seventh photon pair as a first input to a fourth beam splitter and a first photon of an eighth photon pair as a second input to the fourth beam splitter that is distinct from the first beam splitter, the second beam splitter, and the third beam splitter, wherein the fourth beam splitter is coupled with a first output channel of the fourth beam splitter and a second output channel of the fourth beam splitter; and
providing a photon output from the third beam splitter in the second output channel of the third beam splitter as a first input to a third fusion gate and a photon output from the fourth beam splitter in the first output channel of the fourth beam splitter as a second input to the third fusion gate.

### Claim 12 (depends on 11)

The method of claim 11, wherein:
the plurality of photons in the GHZ state includes:
second photons of: the first photon pair, the second photon pair, the third photon pair, the fourth photon pair, the fifth photon pair, the sixth photon pair, the seventh photon pair, and the eighth photon pair;
one photon output from the first beam splitter in the first output channel of the first beam splitter; and
one photon output from the fourth beam splitter in the second output channel of the fourth beam splitter.

### Claim 13 (depends on 12)

The method of claim 12, wherein the GHZ state is a 10-photon GHZ state produced using 8 pairs of photons in a Bell state.

### Claim 14 (depends on 12)

The method of claim 12, wherein:
the plurality of photons in the GHZ state further includes:
one photon output from the second fusion gate.

### Claim 15 (depends on 14)

The method of claim 14, wherein the GHZ state is an 11-photon GHZ state produced using 8 pairs of photons in a Bell state.

### Claim 16 (depends on 1)

The method of claim 1, wherein:
the GHZ state is an n-photon GHZ state;
the first fusion gate is a fusion gate in a plurality of fusion gates; and
the method further includes:
detecting, using the plurality of fusion gates, a state of photons provided to the plurality of fusion gates; and
determining whether the state of the photons provided to the plurality of fusion gates is indicative of an n-photon GHZ state.

### Claim at position 17

17-23. (canceled)

### Claim 24

A method, comprising:
receiving a plurality of qubit pairs, each qubit pair being in a Bell state and including a first qubit and a second qubit that is distinct and separate from the first qubit; and
obtaining a plurality of qubits comprising at least six qubits in a Greenberger-Horn-Zeilinger (GHZ) state by:
providing qubits of the plurality of qubit pairs to a plurality of beam splitters, including:
providing a first mode of a first qubit pair as a first input to a first beam splitter and a first mode of a second qubit pair as a second input to the first beam splitter, wherein the first beam splitter is coupled with a first output channel of the first beam splitter and a second output channel of the first beam splitter; and
providing a first mode of a third qubit pair as a first input to a second beam splitter and a first mode of a fourth qubit pair as a second input to the second beam splitter that is distinct from the first beam splitter, wherein the second beam splitter is coupled with a first output channel of the second beam splitter and a second output channel of the second beam splitter; and
providing a mode output from the first beam splitter in the second output channel of the first beam splitter as a first input to a first detector and a mode output from the second beam splitter in the first output channel of the second beam splitter as a second input to the first detector.

### Claim 25 (depends on 24)

The method of claim 24, wherein:
only one qubit is output from the first beam splitter in the second output channel of the first beam splitter; and
only one qubit is output from the second beam splitter in the first output channel of the second beam splitter.

### Claim 26 (depends on 24)

The method of claim 24, wherein the plurality of qubits in the GHZ state includes:
second qubits of: the first qubit pair, the second qubit pair, the third qubit pair, and the fourth qubit pair.

### Claim 27 (depends on 26)

The method of claim 26, wherein:
the plurality of qubits in the GHZ state includes:
one qubit output from the first beam splitter in the first output channel of the first beam splitter; and
one qubit output from the second beam splitter in the second output channel of the second beam splitter.

### Claim 28 (depends on 27)

The method of claim 27, wherein the GHZ state is a 6-qubit GHZ state produced using 4 pairs of qubits in a Bell state.

### Claim 29 (depends on 24)

The method of claim 24, further including:
detecting, using the first detector, a first state of the qubit provided as the first input to the first detector and a second state of the qubit provided as the second input to the first detector; and
determining whether the first state and the second state are indicative of a 6-qubit GHZ state.

### Claim 30 (depends on 24)

The method of claim 24, wherein:
the first detector includes a first detector and a second detector that is distinct and separate from the first detector; and
the method includes detecting, using the first detector of the first detector, only one qubit selected from the qubit provided as the first input to the first detector and the qubit provided as the second input to the first detector and detecting, using the second detector of the first detector, only another qubit selected from the qubit provided as the first input to the first detector and the qubit provided as the second input to the first detector.

### Claim 31 (depends on 24)

The method of claim 24, further including:
providing a first mode of a fifth qubit pair as a first input to a third beam splitter and a first mode of a sixth qubit pair as a second input to the third beam splitter that is distinct from the first beam splitter and the second beam splitter, wherein the third beam splitter is coupled with a first output channel of the third beam splitter and a second output channel of the third beam splitter; and
providing a qubit output from the second beam splitter in the second output channel of the second beam splitter as a first input to a second detector and a qubit output from the third beam splitter in the first output channel of the third beam splitter as a second input to the second detector.

### Claim 32 (depends on 31)

The method of claim 31, wherein:
the plurality of qubits in the GHZ state includes:
second qubits of: the first qubit pair, the second qubit pair, the third qubit pair, the fourth qubit pair, the fifth qubit pair, and the sixth qubit pair;
one qubit output from the first beam splitter in the first output channel of the first beam splitter; and
one qubit output from the third beam splitter in the second output channel of the third beam splitter.

### Claim 33 (depends on 32)

The method of claim 32, wherein the GHZ state is an 8-qubit GHZ state produced using 6 pairs of qubits in a Bell state.

### Claim 34 (depends on 31)

The method of claim 31, further including:
providing a first mode of a seventh qubit pair as a first input to a fourth beam splitter and a first mode of an eighth qubit pair as a second input to the fourth beam splitter that is distinct from the first beam splitter, the second beam splitter, and the third beam splitter, wherein the fourth beam splitter is coupled with a first output channel of the fourth beam splitter and a second output channel of the fourth beam splitter; and
providing a qubit output from the third beam splitter in the second output channel of the third beam splitter as a first input to a third detector and a qubit output from the fourth beam splitter in the first output channel of the fourth beam splitter as a second input to the third detector.

### Claim 35 (depends on 34)

The method of claim 34, wherein:
the plurality of qubits in the GHZ state includes:
second qubits of: the first qubit pair, the second qubit pair, the third qubit pair, the fourth qubit pair, the fifth qubit pair, the sixth qubit pair, the seventh qubit pair, and the eighth qubit pair;
one qubit output from the first beam splitter in the first output channel of the first beam splitter; and
one qubit output from the fourth beam splitter in the second output channel of the fourth beam splitter.

### Claim 36 (depends on 35)

The method of claim 35, wherein the GHZ state is a 10-qubit GHZ state produced using 8 pairs of qubits in a Bell state.

### Claim 37 (depends on 35)

The method of claim 35, wherein:
the plurality of qubits in the GHZ state further includes:
one qubit output from the second detector.

### Claim 38 (depends on 35)

The method of claim 35, wherein the GHZ state is an 11-qubit GHZ state produced using 8 pairs of qubits in a Bell state.

### Claim 39 (depends on 24)

The method of claim 24, wherein:
the GHZ state is an n-qubit GHZ state;
the first detector is a detector in a plurality of detectors; and
the method further includes:
detecting, using the plurality of detectors, a state of qubits provided to the plurality of detectors; and
determining whether the state of the qubits provided to the plurality of detectors is indicative of an n-qubit GHZ state.

### Claim 40

A method, comprising:
receiving, by a set of 16 qubit inputs, four qubit pairs, each qubit pair being in a Bell state and each Bell state including respective four of the 16 qubit inputs;
coupling four modes, one from each of the four pairs of Bell states;
detecting at least two photons in no less than two of the four coupled modes; and
outputting, on a subset of 12 of 16 waveguides, a plurality of qubits comprising at least six qubits in a Greenberger-Horn-Zeilinger (GHZ) state.

### Claim 41 (depends on 40)

The method of claim 40, wherein for every four Bell states received by the set of 16 qubit inputs, the six qubits in the GHZ state is output with a success probability that is larger than 6.25% and smaller than 18.75%.