# US 2020/0401922 A1 · Qubit assembly having adjustable current operators > Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt - Number: US 2020/0401922 A1 - Document ID: US20200401922A1 - Status: Published application - Kind: A1 - Application number: 16/445,889 - Filed: 2019-06-19 - Published: 2020-12-24 - Earliest claimed: 2019-06-19 - Assignees: Northrop Grumman Systems Corporation - Inventors: DAVID JAMES CLARKE - Web page: https://patentgrep.com/patent/US20200401922A1 ## CPC - H10N 60/805: {for Josephson-effect devices} - G06N 10/40: Physical realisations or architectures of quantum processors or components for manipulating qubits, e.g. qubit coupling or qubit control - H10N 60/12: Josephson-effect devices - H10N: ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR - G06N: COMPUTING ARRANGEMENTS BASED ON SPECIFIC COMPUTATIONAL MODELS ## Abstract A qubit assembly includes a first superconducting loop comprising a first Josephson junction and a second Josephson junction, a second superconducting loop comprising the second Josephson junction and a third Josephson junction, and a third superconducting loop comprising the third Josephson junction and a fourth Josephson junction. A flux source is configured to provide a control flux to the second superconducting loop, such that the effective commutation relations between a first quantum operator corresponding to current in the first superconducting loop and a second quantum operator corresponding to current in the third superconducting loop can be changed by changing a magnitude of the control flux provided to the second superconducting loop by the flux source. ## Claims ### Claim 1 A qubit assembly comprising: a first superconducting loop comprising a first Josephson junction and a second Josephson junction; a second superconducting loop comprising the second Josephson junction and a third Josephson junction; a third superconducting loop comprising the third Josephson junction and a fourth Josephson junction; and a flux source configured to provide a control flux to the second superconducting loop, such that the effective commutation relations between a first quantum operator corresponding to current in the first superconducting loop and a second quantum operator corresponding to current in the third superconducting loop can be changed by changing a magnitude of the control flux provided to the second superconducting loop by the flux source. ### Claim 2 (depends on 1) The qubit assembly of claim 1, wherein the first quantum operator represents a selected X-axis for the qubit assembly and the second quantum operator can be configured to represent an arbitrary axis within a plane of the Bloch sphere by changing a magnitude of the control flux provided to the second superconducting loop. ### Claim 3 (depends on 2) The qubit assembly of claim 2, wherein a quantum operator corresponding to voltage on the superconducting island adjoining the loops represents a third axis within the Bloch sphere perpendicular to each of the X-axis and the arbitrary axis. ### Claim 4 (depends on 1) The qubit assembly of claim 1, wherein the control flux is a first control flux, and the qubit assembly further comprises fourth and fifth superconducting loops, with the fourth loop comprising the first Josephson junction and a fifth Josephson junction and the fifth loop comprising the fifth Josephson junction and a sixth Josephson junction, the flux source being configured to provide a second control flux to the fourth superconducting loop, such that the effective commutation relations between the first quantum operator and a third quantum operator corresponding to current in the fifth superconducting loop can be changed by changing a magnitude of the second control flux. ### Claim 5 (depends on 1) The qubit assembly of claim 1, wherein the first superconducting loop comprises a first path to ground, interrupted by the first Josephson junction, and a second path to ground, interrupted by the second Josephson junction, the second superconducting loop comprises the second path to ground and a third path to ground, interrupted by the third Josephson junction, and the third superconducting loop comprises the third path to ground and a fourth path to ground, interrupted by the fourth Josephson junction. ### Claim 6 (depends on 1) The qubit assembly of claim 1, wherein at least one of the first Josephson junction, the second Josephson junction, the third Josephson junction, and the fourth Josephson junction is a compound Josephson junction. ### Claim 7 (depends on 1) The qubit assembly of claim 1, further comprising a readout resonator coupled to the third superconducting loop and configured to measure a state of the second quantum operator. ### Claim 8 (depends on 1) A system comprising: the qubit assembly of claim 1; and a classical computer configured to record an axis of the Bloch sphere represented by the second quantum operator during each of a plurality of logical operations in which the qubit assembly is engaged. ### Claim 9 (depends on 1) A quantum system comprising: the qubit assembly of claim 1, wherein the flux source is a first flux source and the control flux is a first control flux; and a second qubit assembly comprising: a fourth superconducting loop comprising a fifth Josephson junction and a sixth Josephson junction; a fifth superconducting loop comprising the sixth Josephson junction and a seventh Josephson junction; a sixth superconducting loop comprising the seventh Josephson junction and a eighth Josephson junction; and a second flux source configured to provide a second control flux to the fifth superconducting loop, such that the effective commutation relations between a third quantum operator corresponding to current in one of the fourth superconducting loop and a fourth quantum operator corresponding to current in the sixth superconducting loop can be changed by changing a magnitude of the second control flux; and a coupling assembly configured to couple the third superconducting loop to the sixth superconducting loop. ### Claim 10 (depends on 9) The quantum system of claim 9, wherein the coupling assembly is a tunable coupler comprising a compound Josephson junction. ### Claim 11 A method comprising: coupling a first superconducting loop, associated with a first qubit and having an associated first quantum operator, to a second superconducting loop, associated with a second qubit and having an associated second quantum operator; providing a first control flux to the first qubit to tune the first quantum operator to represent an axis of the Bloch sphere; and providing a second control flux to the second qubit to tune the second quantum operator to represent the axis of the Bloch sphere, such that the first qubit and the second qubit are coupled along the axis of the Bloch sphere associated with the first and second quantum operators. ### Claim 12 (depends on 11) The method of claim 11, wherein providing the first control flux to the first qubit comprises providing the first control flux to a third superconducting loop that shares at least one Josephson junction with the first superconducting loop. ### Claim 13 (depends on 12) The method of claim 12, wherein a the axis of the Bloch sphere represented by the first current operator varies with a value, ϕ, for the first control flux in a manner proportional to COS ( 2  πφ φ 0 )  σ x + sin  ( 2  πφ φ 0 )  σ y . ### Claim 14 (depends on 11) The method of claim 11, coupling the first superconducting loop to the second superconducting loop comprises providing a third control flux to a tunable coupler assembly positioned between the first superconducting loop and the second superconducting loop. ### Claim 15 A system comprising: a first qubit assembly comprising: a first superconducting loop comprising a first Josephson junction and a second Josephson junction; a second superconducting loop comprising the second Josephson junction and a third Josephson junction; a third superconducting loop comprising the third Josephson junction and a fourth Josephson junction; a first flux source configured to provide a first control flux to the second superconducting loop, such that the effective commutation relations between a first quantum operator corresponding to current in the first superconducting loop and a second quantum operator corresponding to current in the third superconducting loop can be changed by changing a magnitude of the first control flux provided to the second superconducting loop by the first flux source; a second qubit assembly comprising: a fourth superconducting loop comprising a fifth Josephson junction and a sixth Josephson junction; a fifth superconducting loop comprising the sixth Josephson junction and a seventh Josephson junction; a sixth superconducting loop comprising the seventh Josephson junction and a eighth Josephson junction; and a second flux source configured to provide a second control flux to the fifth superconducting loop, such that the effective commutation relations between a third quantum operator corresponding to current in one of the fourth superconducting loop and a fourth quantum operator corresponding to current in the sixth superconducting loop can be changed by changing a magnitude of the second control flux; and a coupling assembly configured to couple the third superconducting loop to the sixth superconducting loop. ### Claim 16 (depends on 15) The system of claim 15, wherein the coupling assembly is a first coupling assembly, the system further comprising a third qubit assembly coupled to the first qubit assembly via a second coupling assembly such that an alignment of respective voltage operators associated with the first qubit assembly and the third qubit assembly is energetically favorable. ### Claim 17 (depends on 15) The system of claim 15, wherein the coupling assembly is a first coupling assembly, the system further comprising: a third qubit assembly comprising: a seventh superconducting loop comprising a ninth Josephson junction and a tenth Josephson junction; a eighth superconducting loop comprising the tenth Josephson junction and a eleventh Josephson junction; a ninth superconducting loop comprising the eleventh Josephson junction and a twelfth Josephson junction; and a third flux source configured to provide a third control flux to the eighth superconducting loop, such that the effective commutation relations between a fifth quantum operator corresponding to current in one of the seventh superconducting loop and a sixth quantum operator corresponding to current in the ninth superconducting loop can be changed by changing a magnitude of the third control flux; and a second coupling assembly configured to couple the first superconducting loop to the seventh superconducting loop. ### Claim 18 (depends on 17) The system of claim 17, the system further comprising a fourth qubit assembly coupled to the first qubit assembly via a third coupling assembly such that an alignment of respective voltage operators associated with the first qubit assembly and the fourth qubit assembly is energetically favorable. ### Claim 19 (depends on 15) The system of claim 15, wherein the coupling assembly is a tunable coupler comprising a compound Josephson junction. ### Claim 20 (depends on 15) The system of claim 15, further comprising a classical computer configured to record respective axes of the Bloch sphere represented by each of the second quantum operator and the fourth quantum operator.