Driven kerr nonlinear oscillator and related systems and methods

Patent metadata

Field	Value
Publication number	US-12364169-B2
Application number	US-202318872628-A
Country	US
Kind code	B2
Filing date	Jun 9, 2023
Priority date	Jun 10, 2022
Publication date	Jul 15, 2025
Grant date	Jul 15, 2025

Abstract

Techniques are describing for designing and operating a quantum oscillator. In contrast with conventional approaches to operating a quantum oscillator, the present techniques relate to an oscillator design that has less bare nonlinearity than is conventionally thought to be necessary for efficient operation. Moreover, the oscillator may be driven at a frequency that is detuned away from the frequency at which a nonlinear oscillator is typically driven. In particular, the detuned drive frequency may be substantially different from the typical drive frequency, and furthermore may be a frequency that may be expected to produce a low coherence time without also engineering the reduced nonlinearity described above. As a result, the combination of an engineered reduced nonlinearity combined with a detuned drive may result in a well behaved oscillator with a strong effective nonlinearity that exhibits significantly longer coherence times than conventional quantum oscillators.

First claim

What is claimed is:

1. A method of operating a circuit quantum electrodynamics (cQED) system, the method comprising:
operating at least one energy source to drive a Kerr oscillator at a frequency ω p ,
wherein the Kerr oscillator comprises a plurality of superconducting nonlinear asymmetric inductive elements (SNAILs) coupled to one another in series, each of the plurality of SNAILs comprising a plurality of first Josephson junctions coupled in series and a second Josephson junction coupled in parallel with the plurality of first Josephson junctions, each of the plurality of SNAILS having a transition frequency ω q , and
wherein ω p <2ω q .

2. The method of claim 1 , wherein ω p =2ω q +2Δ, wherein Δ is an integer multiple of −2K, wherein K is a Kerr nonlinearity of the plurality of SNAILs of the Kerr oscillator.

3. The method of claim 1 , further comprising operating the at least one energy source to drive a readout resonator at a frequency ω r −(ω p /2) to thereby produce readout of a quantum state of the Kerr oscillator, wherein the readout resonator is coupled to the plurality of SNAILs of the Kerr oscillator and has a resonant frequency ω r .

4. The method of claim 1 , wherein, within each of the plurality of SNAILs, a tunneling energy of the second Josephson junction is less than a tunneling energy of each of the first Josephson junctions.

5. The method of claim 1 , wherein each of the plurality of SNAILs comprises a superconducting ring connected between two nodes, the superconducting ring comprising:
a first ring portion comprising the plurality of first Josephson junctions connected in series, wherein each second Josephson junction of the plurality of second Josephson junctions has the same tunneling energy; and
a second ring portion comprising the second Josephson junction in parallel with the plurality of first Josephson junctions between the two nodes.

6. The method of claim 5 , further comprising operating one or more magnetic flux generation devices to generate an external DC magnetic flux through the superconducting ring of each of the plurality of SNAILs.

7. The method of claim 6 , wherein the external DC magnetic flux is between 0.25Φ 0 and 0.50Φ 0 , where Φ 0 is the magnetic flux quantum.

8. The method of claim 2 , wherein the frequency ω q is between 5 GHz and 8 GHz.

9. The method of claim 8 , wherein the frequency ω q is between 5.5 GHz and 6.5 GHz.

10. The method of claim 2 , wherein K is between 300 kHz and 400 kHz.

11. The method of claim 10 , wherein K is between 310 kHz and 330 kHz.

12. A circuit quantum electrodynamics (cQED) system comprising:
a Kerr oscillator comprising a plurality of superconducting nonlinear asymmetric inductive elements (SNAILs) coupled to one another in series, each of the plurality of SNAILs comprising a plurality of first Josephson junctions coupled in series and a second Josephson junction coupled in parallel with the plurality of first Josephson junctions, each of the plurality of SNAILS having a transition frequency ω q ; and
an energy source configured to drive the plurality of SNAILs at a frequency ω p , wherein ω p <2ω q .

13. The cQED system of claim 12 , wherein ω p =2ω q +2Δ, wherein Δ is an integer multiple of −2K, wherein K is a Kerr nonlinearity of the plurality of SNAILs of the Kerr oscillator.

14. The cQED system of claim 13 , wherein the frequency ω q is between 5 GHz and 8 GHz.

15. The cQED system of claim 13 , wherein K is between 300 kHz and 400 kHz.

16. The cQED system of claim 12 , further comprising a readout resonator coupled to the plurality of SNAILs of the Kerr oscillator.

17. The cQED system of claim 16 , wherein the readout resonator has a resonant frequency ω r , and the energy source is further configured to drive the readout resonator at a frequency ω r −ω p /2 to thereby produce readout of a quantum state of the Kerr oscillator.

18. The cQED system of claim 12 , further comprising a Purcell filter coupled to the plurality of SNAILs of the Kerr oscillator.

19. The cQED system of claim 12 , wherein, within each of the plurality of SNAILs, the second Josephson junction is characterized by a superconducting phase difference, φ, wherein the SNAIL has a potential that varies as a function of the superconducting phase difference, φ, and has a single potential well, wherein the potential has a non-zero φ 3 term and a φ 4 term that is equal to zero.

20. The cQED system of claim 12 , wherein each of the plurality of SNAILs comprises two first Josephson junctions.

21. The cQED system of claim 12 , wherein, within each of the plurality of SNAILs, the first Josephson junction is formed from two Dolan bridges.

22. The cQED system of claim 12 , wherein, within each of the plurality of SNAILs, a tunneling energy of the second Josephson junction is less than a tunneling energy of each of the first Josephson junctions.

23. The cQED system of claim 22 , wherein the tunneling energy of each first Josephson junction is E J , and the tunneling energy of each second Josephson junction is αE J , where α is less than 0.50 and greater than 0.20.

24. The cQED system of claim 12 , wherein each of the plurality of SNAILs comprises a superconducting ring connected between two nodes, the superconducting ring comprising:
a first ring portion comprising the plurality of first Josephson junctions connected in series, wherein each second Josephson junction of the plurality of second Josephson junctions has the same tunneling energy; and
a second ring portion comprising the second Josephson junction in parallel with the plurality of first Josephson junctions between the two nodes.

25. The cQED system of claim 24 , further comprising one or more magnetic flux generation devices configured to generate an external DC magnetic flux through the superconducting ring of the each of the plurality of SNAILs.

26. The cQED system of claim 25 , wherein the external DC magnetic flux generated by the one or more magnetic flux devices is between 0.25Φ 0 and 0.50Φ 0 , where Φ 0 is the magnetic flux quantum.

27. The cQED system of claim 12 , wherein the Kerr oscillator is formed on a sapphire chip suspended within a cavity.

Assignees

• Univ Yale

Inventors

• Cortiñas Rodrigo G
• Venkatraman Jayameenakshi
• Xiao Xu
• Frattini Nicholas
• Devoret Michel

Classifications

• 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

• B82Y10/00

  Nanotechnology for information processing, storage or transmission, e.g. quantum computing or single electron logic · CPC title

• H10N60/12 Primary

  Josephson-effect devices · CPC title

• B82Y20/00

  Nanooptics, e.g. quantum optics or photonic crystals · CPC title