Multi-qubit tunable coupling architecture using fixed-frequency superconducting qubits

Patent metadata

Field	Value
Publication number	US-2017193388-A1
Application number	US-201514985529-A
Country	US
Kind code	A1
Filing date	Dec 31, 2015
Priority date	Dec 31, 2015
Publication date	Jul 6, 2017
Grant date	—

Abstract

Various embodiments provide a coupling mechanism, method of activation and a square lattice. The coupling mechanism comprises two qubits and a tunable coupling qubit that activates an interaction between the two qubits by modulation of a frequency of the tunable coupling qubit. The tunable coupling qubit capacitively couples the two qubits. The tunable coupling qubit is modulated at a difference frequency of the two qubits. The difference frequency may be significantly larger than an anharmonicity of the two qubits. The tunable coupling qubit may be coupled to the two qubits by two electrodes separated by a superconducting quantum interference device (SQUID) loop having two Josephson junctions or by a single electrode with a SQUID loop coupling to ground. The SQUID loop is controlled by an inductively-coupled flux bias line positioned at the center of the tunable coupling qubit.

First claim

What is claimed is:

1 . A coupling mechanism comprising:
two qubits; and a tunable coupling qubit that activates an interaction between the two qubits by modulation of a frequency of the tunable coupling qubit.

2 . The coupling mechanism of claim 1 , wherein the tunable coupling qubit is modulated at a difference frequency of the two qubits.

3 . The coupling mechanism of claim 2 , wherein the difference frequency of the two qubits is significantly larger than an anharmonicity of the two qubits.

4 . The coupling mechanism of claim 1 , wherein the tunable coupling qubit capacitively couples the two qubits.

5 . The coupling mechanism of claim 1 , wherein the tunable coupling qubit is coupled to the two qubits by two electrodes separated by a superconducting quantum interference device loop having two Josephson junctions.

6 . The coupling mechanism of claim 1 , wherein the tunable coupling qubit is coupled to the two qubits by a single electrode with a superconducting quantum interference device loop coupling to ground.

7 . The coupling mechanism of claim 1 , wherein the superconducting quantum interference device loop is used to control an inductively-coupled flux bias line positioned such that capacitive coupling to two electrodes of the tunable coupling qubit is symmetric.

8 . The coupling mechanism of claim 1 , wherein the exchange-type interaction swaps an excitation between the two qubits.

9 . The coupling mechanism of claim 1 , wherein the exchange-type interaction induces a state-dependent phase shift on one of the two qubits.

10 . The coupling mechanism of claim 1 , wherein the tunable coupling qubit produces a coupling of the two qubits having a strength dependent upon an amplitude of the modulation frequency and a phase dependent upon a phase of the modulation frequency.

11 . The coupling mechanism of claim 1 , wherein the two qubits are transmon type qubits.

12 . The coupling mechanism of claim 1 , wherein the two fixed-frequency qubits are initially decoupled.

13 . The coupling mechanism of claim 1 , wherein the two fixed-frequency qubits are symmetrically positioned mirror qubits and the tunable coupling qubit is positioned between the two qubits.

14 . The coupling mechanism of claim 1 , wherein the two qubits are fixed-frequency qubits.

15 . A method of activating a coupling mechanism comprising:
positioning a tunable coupling qubit between two qubits; and modulating a frequency of the tunable coupling qubit.

16 . The method of claim 15 , wherein the tunable coupling qubit is modulated at a difference frequency of the two qubits.

17 . The method of claim 16 , wherein the difference frequency of the two qubits is significantly larger than an anharmonicity of the two qubits.

18 . The method of claim 15 , wherein the tunable coupling qubit is coupled to the two qubits by two electrodes separated by a superconducting quantum interference device loop having two Josephson junctions.

19 . The method of claim 15 , further comprising using the coupling mechanism as a basis of a universal quantum computer that uses error correction.

20 . The method of claim 15 , further comprising using the coupling mechanism as a platform for quantum simulation of systems interacting based on a lattice of qubits connected via coupling elements mediating interactions between nearest neighbor pairs of qubits.

21 . The method of claim 20 , wherein the systems are interacting via a Heisenberg XYZ interaction.

22 . The method of claim 15 , wherein one of the two qubits is a low-coherence transmon, can be used, the method further comprises swapping excitations to the low-coherence transmon such that initial thermal excitations of the low-coherence transmon are transferred into the environment to cool the qubit.

23 . The method of claim 15 , wherein one of the two qubits is in an excited state, the method further comprises resetting the one of the two qubits to its ground state.

24 . A square lattice comprising:
a plurality of unit cells, each unit cell comprising:
two or more qubits; and
a tunable coupling qubit that activates an interaction between a pair of qubits of the two or more qubits by modulation of a frequency of the tunable coupling qubit.

25 . A quantum gate comprising:
two superconducting qubits; and a tunable coupling qubit that activates an interaction between the two superconducting qubits by modulation of a frequency of the tunable coupling qubit.

Assignees

• IBM

Inventors

• FILIPP Stefan
• Gambetta Jay

Classifications

• G06F15/82

  data or demand driven · CPC title

• G06N99/002 Primary

  Physics · mapped topic

• G06N10/40 Primary

  Physical realisations or architectures of quantum processors or components for manipulating qubits, e.g. qubit coupling or qubit control · CPC title