Josephson nonlinear circuit

Patent metadata

Field	Value
Publication number	US-11791818-B2
Application number	US-202017423631-A
Country	US
Kind code	B2
Filing date	Jan 15, 2020
Priority date	Jan 17, 2019
Publication date	Oct 17, 2023
Grant date	Oct 17, 2023

Abstract

Parametrically pumped four-wave mixing is a key building block for many developments in the field of superconducting quantum information processing. However, undesired frequency shifts such as Kerr, cross-Ken and Stark shifts inherent with four-wave mixing, lead to difficulties in tuning up the desired parametric processes and, for certain applications, severely limit the fidelities of the resulting operations. Some embodiments include a Josephson four-wave mixing device consisting of a SQUID transmon coupled to a half-flux biased SNAIL transmon, a.k.a. capacitively shunted flux qubit. When the two transmon have matching frequencies, an interference effect cancels the negative Kerr of the SQUID transmon with the positive Kerr of the SNAIL transmon while preserving parametric four-wave mixing capabilities.

First claim

What is claimed is:

1. A nonlinear superconducting circuit:
a first nonlinear superconducting device with a potential having a positive anharmonicity;
a second nonlinear superconducting device coupled to the first nonlinear superconducting device, wherein:
the second nonlinear superconducting device has a potential with a negative anharmonicity; and
a resonant frequency of the first nonlinear superconducting device is equal to a resonant frequency of the second nonlinear superconducting device.

2. The nonlinear superconducting circuit of claim 1 , further wherein an inductance of the first nonlinear superconducting device is equal to an inductance of the second nonlinear superconducting device.

3. The nonlinear superconducting circuit of claim 1 , wherein the first nonlinear superconducting device is one of a superconducting nonlinear asymmetric inductive element (SNAIL), a fluxonium qubit, or a radio frequency (RF) superconducting quantum interference device (SQUID), and the second nonlinear superconducting device is one of a transmon, a SQUID, or a SNAIL.

4. The nonlinear superconducting circuit of claim 1 , wherein a resonant frequency of the first nonlinear superconducting device and/or a resonant frequency of the second nonlinear superconducting device is controlled using at least one magnet.

5. The nonlinear superconducting circuit of claim 4 , wherein the first nonlinear superconducting device comprises a loop enclosing a first area and the second nonlinear superconducting device comprises a loop enclosing a second area different from the first area.

6. The nonlinear superconducting circuit of claim 1 , further comprising a cavity, wherein the cavity is a three-dimensional resonator, and wherein the first nonlinear superconducting device and the second nonlinear superconducting device are coupled to the cavity.

7. The nonlinear superconducting circuit of claim 6 , wherein the first nonlinear superconducting device and the second nonlinear superconducting device are capacitively coupled to the cavity.

8. The nonlinear superconducting circuit of claim 6 , wherein:
the first nonlinear superconducting device comprises a first antenna configured to couple the first nonlinear superconducting device to the cavity; and
the second nonlinear superconducting device comprises a second antenna configured to couple the second nonlinear superconducting device to the cavity.

9. The nonlinear superconducting circuit of claim 8 , further comprising a superconducting connecting member that connects a portion of the first antenna to a portion of the second antenna, and wherein:
the first antenna comprises a first antenna portion and a second antenna portion physically connected to opposite sides of the first nonlinear superconducting device; and
the second antenna comprises a third antenna portion and a fourth antenna portion physically connected to opposite sides of the second nonlinear superconducting device.

10. The nonlinear superconducting circuit of claim 6 , wherein the first nonlinear superconducting device is coupled to the second nonlinear superconducting device such that the nonlinear superconducting circuit exhibits a symmetric mode and an asymmetric mode, wherein the symmetric mode couples linearly to the cavity and the asymmetric mode does not couple linearly to the cavity, or the asymmetric mode couples linearly to the cavity and the symmetric mode does not couple linearly to the cavity.

11. The nonlinear superconducting circuit of claim 1 , wherein a magnitude g 4 of the first nonlinear superconducting device is equal to a magnitude of g 4 of the second nonlinear superconducting device.

12. The nonlinear superconducting circuit of claim 1 , wherein a quartic coefficient of the potential of the first nonlinear superconducting device is equal to a quadratic coefficient of the potential of the first nonlinear superconducting device, wherein the quartic coefficient is an effective quartic coefficient that is a function of the quadratic coefficient, a cubic coefficient and a quartic coefficient of the potential of the first nonlinear superconducting device.

13. The nonlinear superconducting circuit of claim 1 , wherein the first nonlinear superconducting device is a SNAIL comprising:
a single small Josephson junction; and
a plurality of large Josephson junctions, wherein a tunneling energy of the small Josephson junction is a fraction, a, of a tunneling energy of each of the plurality of large Josephson junctions.

14. The nonlinear superconducting circuit of claim 13 , or any other preceding claim wherein the fraction, a, is greater than zero and less than 0.50.

15. The nonlinear superconducting circuit of claim 13 , wherein the plurality of large Josephson junctions consists of exactly three Josephson junctions.

16. The nonlinear superconducting circuit of claim 13 , wherein:
the plurality of large Josephson junctions consists of N Josephson junctions; and
the fraction, α, is in a range from 1/N to

1
2

⁢

(

1
N

+

1

N
3

)

.

17. A method of controlling a nonlinear superconducting circuit comprising a first nonlinear superconducting device and a second nonlinear superconducting device, the method comprising:
driving the first nonlinear superconducting device and the second nonlinear superconducting device to produce a Hamiltonian with least one off-diagonal interaction and diagonal interactions equal to zero.

18. The method of claim 17 , wherein driving the first nonlinear superconducting device and the second nonlinear superconducting device comprises using microwave signals.

19. The method of claim 18 , wherein:
the nonlinear superconducting circuit further comprises a cavity, wherein the cavity is a three-dimensional resonator;
the first and second nonlinear superconducting devices are coupled to the cavity; and
the microwave signals are supported by the cavity.

20. The method of claim 19 , further comprising:
coupling the first nonlinear superconducting device to the cavity using a first antenna; and
coupling the second nonlinear superconducting device to the cavity using a second antenna.

21. The method of claim 17 , further comprising applying an external magnetic field to control a resonance frequency of the first nonlinear superconducting device and/or the second nonlinear superconducting device.

22. The method of claim 17 , further comprising driving the nonlinear superconducting circuit such that the nonlinear superconducting circuit exhibits a symmetric mode and an asymmetric mode.

23. The method of claim 22 , wherein the symmetric mode couples linearly to the cavity and the asymmetric mode does not couple linearly to the cavity.

Assignees

• Univ Yale

Inventors

• Mundhada Shantanu
• Frattini Nicholas
• Puri Shruti
• Shankar Shyam
• Girvin Steven M
• Devoret Michel

Classifications

• H03K17/92 Primary

  by the use, as active elements, of superconductive devices · CPC title

• H10N69/00

  Integrated devices, or assemblies of multiple devices, comprising at least one superconducting element covered by group H10N60/00 · CPC title

• G06N10/00

  Quantum computing, i.e. information processing based on quantum-mechanical phenomena · CPC title

• H10N60/805

  for Josephson-effect devices · CPC title

• G06N10/40 Primary

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