International Business Machines Corporation

Aaron Finck

John Ray Blair

April Carniol

John Blair

Oliver Dial

Muir Kumph

Jiri Stehlik

George Andrew Keefe

Techniques and couplers for managing coupling between qubits are presented. A first tuneable coupler qubit (TCQ) can comprise a first frequency mode and a second frequency mode. A second TCQ can comprise a third frequency mode and a fourth frequency mode. First TCQ can be selectively coupled to a first qubit based on the first frequency mode and selectively coupled to the second TCQ based on the second and third frequency modes. Second TCQ can be selectively coupled to a second qubit based on the fourth frequency mode. When certain respective magnetic fluxes are applied to first and second TCQs, ZZ interaction between the first and second qubits can be suppressed. When respective modified magnetic fluxes are applied to first and second TCQs to excite respective frequency modes, coupling can occur, and ZZ interaction and an entangled gate can be created between the first and second qubits.

Multi-mode couplers for enhanced connectivity

One or more electronic systems, electronic structures and/or methods provided herein relate to quantum state measurement while suppressing measurement-induced state transition in a superconducting qubit. An electronic system can comprise a superconducting qubit coupled to a tunable coupler qubit (TCQ), and a microwave drive port coupled to the TCQ. A resonator can be coupled between the TCQ and the microwave drive port. The resonator can be coupled to the microwave drive port by direct capacitive coupling or inductive coupling. The superconducting qubit can be coupled to the TCQ by a pair of parallelly-arranged coupling capacitors having equal capacitance to one another, or the resonator can be coupled to the TCQ by a pair of parallelly-arranged coupling capacitors having equal capacitance to one another.

Suppressing superconducting qubit measurement-induced state transitions

Systems and techniques that facilitate mode-selective couplers for frequency collision reduction are provided. In various embodiments, a device can comprise a control qubit. In various aspects, the device can comprise a first target qubit coupled to the control qubit by a first mode-selective coupler. In various instances, the first mode-selective coupler can facilitate A-mode coupling between the control qubit and the first target qubit. In various embodiments, the device can comprise a second target qubit coupled to the control qubit by a second mode-selective coupler. In various aspects, the second mode selective coupler can facilitate B-mode coupling between the control qubit and the second target qubit. In various embodiments, the first mode-selective coupler can comprise a capacitor that capacitively couples a middle capacitor pad of the control qubit to a middle capacitor pad of the first target qubit. In various embodiments, the second mode-selective coupler can comprise a first capacitor that capacitively couples an end capacitor pad of the control qubit to an end capacitor pad of the first target qubit and can comprise a second capacitor that capacitively couples the end capacitor pad of the control qubit to a middle capacitor pad of the second target qubit.

Mode-selective couplers for frequency collision reduction

Devices and/or computer-implemented methods to facilitate ZZ cancellation between qubits are provided. According to an embodiment, a device can comprise a coupler device that operates in a first oscillating mode and a second oscillating mode. The device can further comprise a first superconducting qubit coupled to the coupler device based on a first oscillating mode structure corresponding to the first oscillating mode and based on a second oscillating mode structure corresponding to the second oscillating mode. The device can further comprise a second superconducting qubit coupled to the coupler device based on the first oscillating mode structure and the second oscillating mode structure.

Quantum coupler facilitating suppression of ZZ interactions between qubits

Systems and techniques that facilitate mitigating stray-coupling via multi junction qubits are provided. In various embodiments, a device can comprise a first qubit having a plurality of Josephson junctions respectively between a plurality of capacitor pads. In various aspects, the device can further comprise a plurality of second qubits respectively coupled to different ones of the plurality of capacitor pads, such that no two of the plurality of second qubits can be coupled to a same one of the plurality of capacitor pads.

Mitigating stray-coupling via multi-junction qubits

Devices and/or computer-implemented methods facilitating static ZZ suppression and Purcell loss reduction using mode-selective coupling in two junction superconducting qubits are provided. In an embodiment, a device can comprise a superconducting bus resonator. The device can further comprise a first superconducting qubit. The device can further comprise a second superconducting qubit, the first superconducting qubit and the second superconducting qubit respectively comprising: a first superconducting pad; a second superconducting pad; a third superconducting pad; a first Josephson Junction coupled to the first superconducting pad and the second superconducting pad; and a second Josephson Junction coupled to the second superconducting pad and the third superconducting pad. The first superconducting pad and the second superconducting pad of the first superconducting qubit and the second superconducting qubit are coupled to the superconducting bus resonator. The superconducting bus resonator entangles the first superconducting qubit and the second superconducting qubit based on receiving a control signal.

Quantum device facilitating suppression of ZZ interactions between two-junction superconducting qubits

Techniques regarding a quantum entangling gate between multi-mode superconducting qubits are provided. For example, one or more embodiments described herein can comprise an apparatus, which can comprise a first multi-mode superconducting qubit coupled to a second multi-mode superconducting qubit via a transmon qubit.

Quantum entangling gate between multi-mode qubits

A qubit structure includes a first fluxonium qubit having a first Josephson Junction (JJ) in parallel with a first capacitor and a first superconducting inductor. A second fluxonium qubit includes a second JJ in parallel with a second capacitor and a second superconducting inductor, coupled in series with the first fluxonium qubit. A third capacitor is coupled in parallel to the series first and second fluxonium qubits.

Multi-qubit architectures with mode-selective charge coupling between novel fluxonium-molecule qubits

A device comprises first and second qubits, and a qubit coupler coupled between the first and second qubits. The second qubit comprises first and second modes with the first mode configured to store data. The qubit coupler comprises first and second modes, and operates in a first state or second state. In the first state, the first qubit is exchange coupled to the first mode of the qubit coupler, and the second mode of the second qubit is exchange coupled to the second mode of the qubit coupler, to suppress interaction between the first and second qubits. In the second state, the first qubit and the first mode of the second qubit are exchange coupled to both the first and second modes the qubit coupler, to enable interaction between the first and second qubits for an entanglement gate operation in response to a control signal applied to the qubit coupler.

Multimode coupler to control interaction between quantum bits

Systems and techniques that facilitate entanglement via driving dark modes are provided. In various embodiments, a method can comprise accessing a first multi-mode qubit and a second multi-mode qubit. In various cases, the first multi-mode qubit can be coupled to the second multi-mode qubit by a mode-selective coupler. In various aspects, the method can further comprise exciting a dark mode of the first multi-mode qubit. In various cases, the exciting the dark mode can entangle the first multi-mode qubit with the second multi-mode qubit.

Driving dark modes to facilitate entanglement

Devices and/or computer-implemented methods facilitating static ZZ suppression and Purcell loss reduction using mode-selective coupling in two-junction superconducting qubits are provided. In an embodiment, a device can comprise a superconducting bus resonator. The device can further comprise a first superconducting qubit. The device can further comprise a second superconducting qubit, the first superconducting qubit and the second superconducting qubit respectively comprising: a first superconducting pad; a second superconducting pad; a third superconducting pad; a first Josephson Junction coupled to the first superconducting pad and the second superconducting pad; and a second Josephson Junction coupled to the second superconducting pad and the third superconducting pad. The first superconducting pad and the second superconducting pad of the first superconducting qubit and the second superconducting qubit are coupled to the superconducting bus resonator. The superconducting bus resonator entangles the first superconducting qubit and the second superconducting qubit based on receiving a control signal.

A method of detecting leakage of a data qubit includes applying a first cross-resonance pulse to the data qubit, the data qubit including a first state and a second state; applying a first echo pulse to the data qubit temporally following the applied first cross-resonance pulse; applying a second cross-resonance pulse to the data qubit temporally following the applied first echo pulse, the second cross-resonance pulse being an inverted form of the first cross-resonance pulse; applying a second echo pulse to the data qubit temporally following the second cross-resonance pulse; and detecting a leakage associated with the data qubit using an ancilla qubit coupled to the data qubit based on application of the first and second cross-resonance pulses, and the first and second echo pulses.

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Aaron Finck