IP Library › Granted Patent US 12664454

Granted Patent B2

US 12664454 · App. 17/626,967 · Granted Jun 23, 2026

Superconducting circuit and quantum computer

Inventors: Masahiro Hasegawa (Tokyo, JP); Tsuyoshi Yamamoto (Tokyo, JP); Yoshihito Hashimoto (Tokyo, JP)

Assignee: NEC CORPORATION

G06N10/40 G06N10/60 H03K17/92 H10N69/00

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Quick Facts

Patent No.: US 12664454
App. No.: 17/626,967
Granted: Jun 23, 2026
Kind: B2

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Abstract

A superconducting circuit and a quantum computer capable of implementing four-body interaction while reducing an amount of hardware are provided. A superconducting circuit ( 1 ) includes four superconducting qubit circuits ( 10 ), a coupling circuit ( 20 ) inductively coupled to the four superconducting qubit circuits ( 10 ). Each of the superconducting qubit circuits ( 10 ) indicates a qubit by being in a first phase state or a second phase state, when the number of the superconducting qubit circuits ( 10 ) in the first phase state among the four superconducting qubit circuits ( 10 ) is an even number, an interaction term of Hamiltonian of the superconducting circuit ( 1 ) takes a first value, and when the number of the superconducting qubit circuits ( 10 ) in the first phase state among the four superconducting qubit circuits ( 10 ) is an odd number, the interaction term takes a second value.

Claims (105)

1 . A superconducting circuit comprising:

four superconducting qubit circuits; and

a coupling circuit inductively coupled to the four superconducting qubit circuits,

wherein each of the four superconducting qubit circuits indicates a qubit by being in a first phase state or a second phase state,

wherein, when the number of the four superconducting qubit circuits in the first phase state among the four superconducting qubit circuits is an even number, an interaction term of a Hamiltonian of the superconducting circuit takes a first value,

wherein, when the number of the four superconducting qubit circuits in the first phase state among the four superconducting qubit circuits is an odd number, the interaction term takes a second value,

wherein the coupling circuit comprises four loop circuits independent of each other, each of the four loop circuits comprising an inductor and a Josephson junction, and

wherein the four superconducting qubit circuits are a first superconducting qubit circuit, a second superconducting qubit circuit, a third superconducting qubit circuit, and a fourth superconducting qubit circuit, respectively,

wherein:

the first superconducting qubit circuit is inductively coupled to each of the four loop circuits,

the second superconducting qubit circuit is inductively coupled to each of the four loop circuits,

the third superconducting qubit circuit is inductively coupled to each of the four loop circuits, and

the fourth superconducting qubit circuit is inductively coupled to each of the four loop circuits,

the inductor is a positive direction inductor inductively coupled to any of the four superconducting qubit circuits and is inserted therein so that a current flows in the same direction as a direction of a current in the four loop circuits or a reverse direction inductor inductively coupled to any of the four superconducting qubit circuits and is inserted therein so that a current flows in a direction opposite to the direction of the current in the four loop circuits, and

a combination of types of the inductors used in the inductive coupling between one of the four superconducting qubit circuits and the four loop circuits differs for each of the four superconducting qubit circuits,

in the i-th loop circuit, where i is any integer from 1 to 4, among the four loop circuits, the Josephson junction is provided between two adjacent ones of the inductors, the two adjacent ones of the inductors being composed of the inductor inductively coupled to the j-th superconducting qubit circuit, where j is any integer from 1 to 4 , among the four superconducting qubit circuits and the inductor inductively coupled to the k-th superconducting qubit circuit, where k is an integer from 1 to 4, and j and k have values different from each other, among the four superconducting qubit circuits, and

in the four loop circuits other than the i-th loop circuit among the four loop circuits, the Josephson junction is provided at a position other than between the two adjacent ones of the inductors composed of the inductor inductively coupled to the j-th superconducting qubit circuit among the four superconducting qubit circuits and the inductor inductively coupled to the k-th superconducting qubit circuit among the four superconducting qubit circuits.

2 . A superconducting circuit comprising:

four superconducting qubit circuits; and

a coupling circuit inductively coupled to the four superconducting qubit circuits,

wherein each of the four superconducting qubit circuits indicates a qubit by being in a first phase state or a second phase state,

wherein, when the number of the four superconducting qubit circuits in the first phase state among the four superconducting qubit circuits is an odd number, the interaction term takes a second value,

wherein the coupling circuit comprises four loop circuits independent of each other, each of the four loop circuits comprising an inductor and a Josephson junction, and

wherein:

the first superconducting qubit circuit is inductively coupled to each of the four loop circuits,

the second superconducting qubit circuit is inductively coupled to each of the four loop circuits,

the third superconducting qubit circuit is inductively coupled to each of the four loop circuits, and

the fourth superconducting qubit circuit is inductively coupled to each of the four loop circuits,

the interaction term of the Hamiltonian of the superconducting circuit is expressed by the following formula, wherein q 1 is a phase of the first superconducting qubit circuit and indicates the first phase state or the second phase state, φ 2 is a phase of the second superconducting qubit circuit and indicates the first phase state or the second phase state, φ 3 is a phase of the third superconducting qubit circuit and indicates the first phase state or the second phase state, φ 4 is a phase of the fourth superconducting qubit circuit and indicates the first phase state or the second phase state, E J is Josephson energy of the Josephson junction, and M is a mutual inductance between the four superconducting qubit circuits and the four loop circuits:

E J cos[ M (φ 1 +φ 2 +φ 3 −φ 4 )]+ E J cos[ M (φ 1 +φ 2 −φ 3 +φ 4 )]+ E J cos[ M (φ 1 −φ 2 +φ 3 +φ 4 )]+ E J cos[ M (−φ 1 +φ 2 +φ 3 +φ 4 )]

3 . The superconducting circuit according to claim 2 , wherein:

the four loop circuits are a first loop circuit, a second loop circuit, a third loop circuit, and a fourth loop circuit, respectively,

the first loop circuit includes:

the positive direction inductor inductively coupled to the first superconducting qubit circuit;

the positive direction inductor inductively coupled to the second superconducting qubit circuit;

the positive direction inductor inductively coupled to the third superconducting qubit circuit; and

the positive direction inductor inductively coupled to the fourth superconducting qubit circuit,

the second loop circuit includes:

the positive direction inductor inductively coupled to the first superconducting qubit circuit;

the positive direction inductor inductively coupled to the second superconducting qubit circuit;

the reverse direction inductor inductively coupled to the third superconducting qubit circuit; and

the reverse direction inductor inductively coupled to the fourth superconducting qubit circuit,

the third loop circuit includes:

the positive direction inductor inductively coupled to the first superconducting qubit circuit;

the reverse direction inductor inductively coupled to the second superconducting qubit circuit;

the positive direction inductor inductively coupled to the third superconducting qubit circuit; and

the reverse direction inductor inductively coupled to the fourth superconducting qubit circuit, and

the fourth loop circuit includes:

the positive direction inductor inductively coupled to the first superconducting qubit circuit;

the reverse direction inductor inductively coupled to the second superconducting qubit circuit;

the reverse direction inductor inductively coupled to the third superconducting qubit circuit; and

the positive direction inductor inductively coupled to the fourth superconducting qubit circuit.

4 . A superconducting circuit comprising:

four superconducting qubit circuits; and

a coupling circuit inductively coupled to the four superconducting qubit circuits,

wherein each of the four superconducting qubit circuits indicates a qubit by being in a first phase state or a second phase state,

wherein, when the number of the four superconducting qubit circuits in the first phase state among the four superconducting qubit circuits is an odd number, the interaction term takes a second value,

wherein the coupling circuit comprises four loop circuits independent of each other, each of the four loop circuits comprising an inductor and a Josephson junction, and

wherein:

the first superconducting qubit circuit is inductively coupled to each of the four loop circuits,

the second superconducting qubit circuit is inductively coupled to each of the four loop circuits,

the third superconducting qubit circuit is inductively coupled to each of the four loop circuits, and

the fourth superconducting qubit circuit is inductively coupled to each of the four loop circuits,

the interaction term of the Hamiltonian of the superconducting circuit is expressed by the following formula, wherein φ 1 is a phase of the first superconducting qubit circuit and indicates the first phase state or the second phase state, φ 2 is a phase of the second superconducting qubit circuit and indicates the first phase state or the second phase state, φ 3 is a phase of the third superconducting qubit circuit and indicates the first phase state or the second phase state, φ 4 is a phase of the fourth superconducting qubit circuit and indicates the first phase state or the second phase state, E j is Josephson energy of the Josephson junction, and M is a mutual inductance between the four superconducting qubit circuits and the four loop circuits:

E J cos[ M (φ 1 +φ 2 +φ 3 −φ 4 )]+ E J cos[ M (φ 1 +φ 2 −φ 3 +φ 4 )]+ E J cos[ M (φ 1 −φ 2 +φ 3 +φ 4 )]+ E J cos[ M (−φ 1 +φ 2 +φ 3 +φ 4 )]

5 . The superconducting circuit according to claim 4 , wherein:

the four loop circuits are a first loop circuit, a second loop circuit, a third loop circuit, and a fourth loop circuit, respectively,

the first loop circuit includes:

the reverse direction inductor inductively coupled to the first superconducting qubit circuit;

the positive direction inductor inductively coupled to the second superconducting qubit circuit;

the positive direction inductor inductively coupled to the third superconducting qubit circuit; and

the positive direction inductor inductively coupled to the fourth superconducting qubit circuit,

the second loop circuit includes:

the positive direction inductor inductively coupled to the first superconducting qubit circuit;

the reverse direction inductor inductively coupled to the second superconducting qubit circuit;

the positive direction inductor inductively coupled to the third superconducting qubit circuit; and

the positive direction inductor inductively coupled to the fourth superconducting qubit circuit,

the third loop circuit includes:

the positive direction inductor inductively coupled to the first superconducting qubit circuit;

the positive direction inductor inductively coupled to the second superconducting qubit circuit;

the reverse direction inductor inductively coupled to the third superconducting qubit circuit; and

the positive direction inductor inductively coupled to the fourth superconducting qubit circuit, and

the fourth loop circuit includes:

the positive direction inductor inductively coupled to the first superconducting qubit circuit;

the positive direction inductor inductively coupled to the second superconducting qubit circuit;

the positive direction inductor inductively coupled to the third superconducting qubit circuit; and

the reverse direction inductor inductively coupled to the fourth superconducting qubit circuit.

6 . A quantum computer comprising, as a unit structure, the superconducting circuit according to claim 1 .

7 . The quantum computer according to claim 6 comprising:

a plurality of the unit structures,

wherein one or more of the four superconducting qubit circuits is shared by the plurality of the unit structures.

8 . The quantum computer according to claim 7 , wherein:

the coupling circuit includes a rectangular shape, and

the one or more of the four superconducting qubit circuits is shared by the plurality of unit structures by being arranged close to each vertex of the rectangular shape.

9 . The quantum computer according to claim 7 , wherein:

the coupling circuit includes a cross shape, and

the one or more of the four superconducting qubit circuits is shared by the plurality of unit structures by being arranged close to ends of the cross shape projecting outward.