Josephson phase-slip qubits

Patent metadata

Field	Value
Publication number	US-10735003-B2
Application number	US-201916580215-A
Country	US
Kind code	B2
Filing date	Sep 24, 2019
Priority date	Sep 27, 2018
Publication date	Aug 4, 2020
Grant date	Aug 4, 2020

Abstract

A qubit includes a superconducting loop interrupted by a plurality of magnetic flux tunneling elements, such as DC SQUIDs, leaving superconducting islands between the elements. An effective transverse magnetic moment is formed by magnetically tuning each element to yield a large tunneling amplitude. The electrical polarization charge on an island is tuned to produce destructive interference between the tunneling amplitudes using the Aharonov-Casher effect, resulting in an effectively zero transverse field. Biasing the charge away from this tuning allows tunneling to resume with a large amplitude. Interrupting the island with a third tunneling path, such as a Josephson junction, permits independently tuning and biasing the two islands that result, enabling effective control of two independent (X and Y) transverse fields.

First claim

What is claimed is:

1. A qubit comprising a superconductor arranged in a loop that is interrupted by a plurality of tunneling circuits for tunneling magnetic fluxons between the interior and exterior of the loop according to respective tunneling amplitudes, at least one such tunneling amplitude being magnetically tunable, and at least one island in a portion of the loop between the tunneling circuits being electrically biasable to adjust relative phases between the tunneling amplitudes.

2. The qubit according to claim 1 , wherein at least two of the plurality of tunneling circuits each comprise a direct current superconducting quantum interference device (DC SQUID).

3. The qubit according to claim 2 , wherein each such DC SQUID comprises a superconductor arranged in a second loop that is interrupted by two Josephson junctions, the DC SQUID being magnetically tunable by varying a magnetic flux passing through the second loop.

4. The qubit according to claim 2 , wherein an island in the loop between two of the DC SQUIDs is electrically biased with an excess electrical charge to thereby emulate a zero transverse field.

5. The qubit according to claim 4 , wherein the excess electrical charge is approximately that of one electron.

6. The qubit according to claim 4 , further comprising a coupler for electrically coupling to the island to produce a transverse electric dipole moment.

7. The qubit according to claim 4 , wherein the two DC SQUIDs are magnetically biased so that coupling an additional magnetic flux to the two DC SQUIDs in either a differential mode or a common mode emulates coupling to a transverse magnetic moment.

8. The qubit according to claim 4 , wherein the plurality of tunneling circuits further comprises a third, non-tunable fluxon tunneling circuit, and wherein a second island in the loop is electrically biased with a second excess electrical charge to thereby emulate the zero transverse field.

9. The qubit according to claim 8 , wherein the excess electrical charge and the second excess electrical charge each are approximately two-thirds of one electron.

10. The qubit according to claim 8 , wherein magnetic coupling to the common and differential modes of the two DC SQUID fluxes produces two orthogonal transverse magnetic dipole moments.

11. The qubit according to claim 8 , wherein electrical coupling to the common and differential modes of the two island charges produces two orthogonal transverse electric dipole moments.

12. A method of operating a qubit comprising a superconductor arranged in a loop that is interrupted by a plurality of tunneling circuits for tunneling magnetic fluxons between the interior and exterior of the loop according to respective tunneling amplitudes, the method comprising:
electrically biasing an island in a portion of the loop between two of the tunneling circuits to adjust relative phases between the tunneling amplitudes of the two tunneling circuits; and
magnetically tuning either or both of the two tunneling circuits.

13. The method according to claim 12 , wherein the two tunneling circuits each comprise a direct current superconducting quantum interference device (DC SQUID).

14. The method according to claim 13 , wherein magnetically tuning either DC SQUID comprises varying a magnetic flux passing through a superconducting loop of the DC SQUID.

15. The method according to claim 13 , wherein electrically biasing includes biasing with an excess electrical charge to thereby emulate a zero transverse field.

16. The method according to claim 15 , wherein the excess electrical charge is approximately that of one electron.

17. The method according to claim 15 , further comprising electrically coupling to the island to produce a transverse electric dipole moment.

18. The method according to claim 15 , further comprising magnetically biasing the two DC SQUIDs so that coupling an additional magnetic flux to the two DC SQUIDs in either a differential mode or a common mode emulates coupling to a transverse magnetic moment.

19. The method according to claim 15 , wherein the plurality of tunneling circuits further comprises a third, non-tunable fluxon tunneling circuit, the method further comprising electrically biasing a second island in the loop with a second excess electrical charge to thereby emulate the zero transverse field.

20. The method according to claim 19 , wherein the excess electrical charge and the second excess electrical charge each are approximately two-thirds of one electron.

21. The method according to claim 19 , further comprising magnetically coupling to common and differential modes of the two DC SQUID fluxes to produce two orthogonal transverse magnetic dipole moments.

22. The method according to claim 19 , further comprising electrically coupling to common and differential modes of the two island charges to produce two orthogonal transverse electric dipole moments.

Assignees

• Massachusetts Inst Technology
• Mssachusetts Institute Of Tech

Inventors

• Kerman Andrew J

Classifications

• H03K19/1952 Primary

  with electro-magnetic coupling of the control current · CPC title

• G06N10/00

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