Northrop Grumman Systems Corporation

Zachary Keane

Ofer Naaman

David George Ferguson

Joel D Strand

Micah John Atman Stoutimore

Jeffrey David Hartman

Aurelius L Graninger

Justin C Hackley

John Xavier Przybysz

Robert Miles Young

Aaron Ashley Hathaway

James Redding Medford

Greg Boyd

Micah Stoutimore

Test structures and methods for superconducting bump bond electrical characterization are used to verify the superconductivity of bump bonds that electrically connect two superconducting integrated circuit chips fabricated using a flip-chip process, and can also ascertain the self-inductance of bump bond(s) between chips. The structures and methods leverage a behavioral property of superconducting DC SQUIDs to modulate a critical current upon injection of magnetic flux in the SQUID loop, which behavior is not present when the SQUID is not superconducting, by including bump bond(s) within the loop, which loop is split among chips. The sensitivity of the bump bond superconductivity verification is therefore effectively perfect, independent of any multi-milliohm noise floor that may exist in measurement equipment.

Superconducting bump bond electrical characterization

A capacitively-driven tunable coupler includes a coupling capacitor connecting an open end of a quantum object (i.e., an end of the object that cannot have a DC path to a low-voltage rail, such as a ground node, without breaking the functionality of the object) to an RF SQUID having a Josephson element capable of providing variable inductance and therefore variable coupling to another quantum object.

Capacitively-driven tunable coupling

A superconductor thermal filter is disclosed that includes a normal metal layer having a first side, an insulating layer overlying the first side of the normal metal layer, and a multilayer superconductor structure having a first side overlying a side of the insulating layer opposite the side that overlies the normal metal layer. The multilayer superconductor structure is comprised of a plurality of superconductor layers with each superconductor layer having a smaller superconducting energy band gap than the preceding superconductor as the superconductor layers extend away from the normal metal layer. The thermal filter further includes a normal metal layer quasiparticle trap having a first side and a second side with the first side being disposed on a second side of the multilayer superconductor. A bias voltage is applied between the normal metal layer and the normal metal layer quasiparticle trap to remove hot electrons from the normal metal layer.

Superconductor thermal filter

Real-time reconfigurability of quantum object connectivity can be provided with one or more quantum routers that can each be configured as either or both of a single-pole double-throw switch and a cross-point switch. The quantum router includes variable-inductance coupling elements in RF-SQUIDs having inductors transformer-coupled to two control flux lines, one providing a static current and the other providing a dynamic current, the direction of which can be toggled to couple or uncouple quantum objects, such as qubits, based on the dynamic current direction to provide reconfigurable quantum routing.

Reconfigurable quantum routing

A tunable bus-mediated coupling system is provided that includes a first input port coupled to a first end of a variable inductance coupling element through a first resonator and a second input port coupled to a second end of the variable inductance coupling element through a second resonator. The first input port is configured to be coupled to a first qubit, and the second output port is configured to be coupled to a second qubit. A controller is configured to control the inductance of the variable inductance coupling element between a low inductance state to provide strong coupling between the first qubit and the second qubit and a high inductance state to provide isolation between the first qubit and the second qubit.

Tunable bus-mediated coupling between remote qubits

A load-compensated tunable coupler leverages a cross-bar switch and simulated loads or ballasts to provide a tunable coupling between two quantum objects that can be selectively coupled or decoupled without changing their resonant frequencies.

Load-compensated tunable coupling

A push-pull tunable coupler includes a push transformer, a pull transformer and two compound Josephson junctions arranged in upper and lower branches. Absent biasing, the balanced push and pull of current between the branches causes current from a first object to circulate within a loop and not to be coupled to a second object. Biasing of at least one of the compound Josephson junctions unbalances the push and pull of current in the branches to couple the first and second objects. The coupler has reduced sensitivity to differential-mode noise around the off state, is completely insensitive to common-mode noise, and is capable of inverting the coupled signal with appropriate relative biasing of the compound Josephson junctions.

Push-pull tunable coupling

Quantum systems are provided, including a qubit and a transmission line resonator having an associated resonant wavelength. A coupling capacitor is configured to capacitively couple the qubit to the transmission line resonator. A transformer is configured to inductively couple the qubit to the transmission line resonator. A selected one of an associated capacitance of the coupling capacitor and an associated mutual inductance of the transformer is a function of a location of the qubit along the transmission line resonator.

Growing community of inventors

Baltimore, MD, United States of America

Zachary Keane