In a new PRA paper, quantum optimal control theory is employed to realize quantum gates for two protected superconducting circuits: the heavy-fluxonium qubit and the 0-π qubit. Utilizing automatic differentiation facilitates the simultaneous inclusion of multiple optimization targets, allowing one to obtain high-fidelity gates with realistic pulse shapes. For both qubits, disjoint support of low-lying […]

Superconducting qubits designed to exhibit protection from noise have recently received attention in the search for a qubit with coherence times that could exceed those of current state-of-the-art qubits. The current-mirror circuit has long been proposed as such a protected qubit. Based on an effective model capturing the low-energy excitations of the circuit, we present […]

Superconducting circuits extensively rely on the Josephson junction as a nonlinear electronic element for manipulating quantum information and mediating photon interactions. Despite continuing efforts in pushing the coherence of Josephson circuits, the best photon lifetimes have been demonstrated in microwave cavities. Nevertheless, architectures based on quantum memories require a qubit element for logical operations at […]

Encoding a qubit in logical quantum states with wavefunctions characterized by disjoint support and robust energies can offer simultaneous protection against relaxation and pure dephasing. Using a circuit-quantum-electrodynamics architecture, we experimentally realize a superconducting 0−π qubit, which hosts protected states suitable for quantum-information processing. Multi-tone spectroscopy measurements reveal the energy level structure of the system, […]

Circuit quantization links a physical circuit to its corresponding quantum Hamiltonian. The standard quantization procedure generally assumes any external magnetic flux to be static. Time dependence naturally arises, however, when flux is modulated or when flux noise is considered. In this case, application of the existing quantization procedure can lead to inconsistencies. To resolve these, […]

In a new PRA manuscript, we present a gradient-based optimal-control technique for open quantum systems that utilizes quantum trajectories to simulate the quantum dynamics during optimization. Using trajectories allows for optimizing open systems with less computational cost than the regular density matrix approaches in most realistic optimization problems. We introduce an improved-sampling algorithm which minimizes […]

In a new collaboration with the Université de Sherbrooke, we have shown that the coherence times of a realistic 0–π device can surpass that of today’s best superconducting qubits (Groszkowski et al 2018 New J. Phys. 20 043053). Here we address controllability of the 0–π qubit. Specifically, we investigate the potential for dispersive control and […]