Open Access publication in J. Phys. Commun.: Optimal control of large quantum systems: assessing memory and runtime performance of GRAPE

Quantum information processing has spurred interest in quantum optimal control for tasks such as state preparation, error correction, and realization of logical gates. Gradient Ascent Pulse Engineering (GRAPE) is a prominent technique for implementing quantum optimal control by adjusting parameters to minimize infidelity in state transfers or gate operations using gradient descent. Many efforts have […]

New arXiv preprint: Crosstalk-Robust Quantum Control in Multimode Bosonic Systems

Superconducting cavities offer a hardware-efficient platform for quantum information processing. Controlling such bosonic modes requires nonlinear elements, for example, transmon ancillae. While a transmon is coupled to multiple cavities, crosstalk happens – the qubit frequency is susceptible to one of the cavity’s state and thus influence the control on other systems. To mitigate such coherent […]

New Quantum Publication: Completely Positive Map for Noisy Driven Quantum Systems Derived by Keldysh Expansion

Decoherence errors, caused by the interaction of quantum systems with their environment, pose a major challenge for the practical implementation of quantum computing. Accurately modeling these errors is essential for analyzing and improving gate fidelities. While Lindblad master equation and its several generalizations have been proposed, there is still ongoing exploration for simpler and more […]

New arXiv preprint: Tunable inductive coupler for high fidelity gates between fluxonium qubits

The fluxonium qubit is a promising candidate for quantum computation due to its long coherence times and large anharmonicity. Our experimental collaborators present the experimental realization of a tunable coupler that realizes strong inductive coupling between two heavy-fluxonium qubits, following our previous theoretical analysis in this paper. The coupler enables the qubits to have a […]

New arXiv preprint: Systematic Improvements in Transmon Qubit Coherence Enabled by Niobium Surface Encapsulation

The inherent interactions between the qubits and their environment lead to decoherence, limiting the performance of these devices. In this paper, we present a novel technique for improving T1 coherence times in transmon qubits by passivating the surface of niobium and preventing the formation of lossy surface oxide. Our comparative investigation across different qubit foundries […]

New arXiv Preprint: Optimal control of large quantum systems: assessing memory and runtime performance of GRAPE

Quantum information processing has spurred interest in quantum optimal control for tasks such as state preparation, error correction, and realization of logical gates. Gradient Ascent Pulse Engineering (GRAPE) is a prominent technique for implementing quantum optimal control by adjusting parameters to minimize infidelity in state transfers or gate operations using gradient descent. Many efforts have […]

New arXiv Preprint: Completely Positive Map for Noisy Driven Quantum Systems Derived by Keldysh Expansion

Decoherence errors, caused by the interaction of quantum systems with their environment, pose a major challenge for the practical implementation of quantum computing. Accurately modeling these errors is essential for analyzing and improving gate fidelities. While Lindblad master equation and its several generalizations have been proposed, there is still ongoing exploration for simpler and more […]

New Quantum publication: Simple master equations for describing driven systems subject to classical non-Markovian noise

Together with theory collaborators from UChicago we analyze driven quantum systems subject to non-Markovian noise. These systems are typically difficult to model even if the noise is classical. We present a systematic method based on generalized cumulant expansions for deriving a time-local master equation for such systems. This master equation has an intuitive form that […]

New Editor’s Suggestion Phys. Rev. Applied publication: Time-Dependent Magnetic Flux in Devices for Circuit Quantum Electrodynamics

The use of time-dependent flux is ubiquitous in the context of circuit quantum electrodynamics. It is critical to accurately model time-dependent flux in circuit Hamiltonians, which is what Xinyuan at al. did in our previous work. Working with Houck lab in Princeton, we provide experimental verification of what the flux allocation should be in the […]

New PRX QUANTUM Publication: Fast High-Fidelity Gates for Galvanically-Coupled Fluxonium Qubits Using Strong Flux Modulation

Along with coworkers from the Schuster lab at UChicago, we introduce a coupling scheme for low frequency fluxonium qubits that allows for high-fidelity entangling gates. Long coherence times, large anharmonicity and robust charge-noise insensitivity render fluxonium qubits an interesting alternative to transmons. Recent experiments have demonstrated record coherence times for low-frequency fluxonia. Here, we propose […]