Experimental Time-Optimal Universal Control of Spin Qubits in Solids

Abstract

Quantum control of systems plays an important role in modern science and technology. The ultimate goal of quantum control is to achieve high-fidelity universal control in a time-optimal way. Although high-fidelity universal control has been reported in various quantum systems, experimental implementation of time-optimal universal control remains elusive. Here, we report the experimental realization of time-optimal universal control of spin qubits in diamond. By generalizing a recent method for solving quantum brachistochrone equations [X. Wang et al., Phys. Rev. Lett. 114, 170501 (2015)], we obtained accurate minimum-time protocols for multiple qubits with fixed qubit interactions and a constrained control field. Single- and two-qubit time-optimal gates are experimentally implemented with fidelities of 99% obtained via quantum process tomography. Our work provides a time-optimal route to achieve accurate quantum control and unlocks new capabilities for the emerging field of time-optimal control in general quantum systems.

Tight, robust, and feasible quantum speed limits for open dynamics

“…The use of this norm has several benefits: It allows for the effective use of optimization techniques, such as convex optimization and semidefinite programming [75], it is easy to manipulate analytically and numerically, it has a straightforward geometric interpretation, and it is independent from the choice of the Lie algebra Λ of SU (d) used to represent states as GBVs. The Hilbert-Schmidt norm is also widely used in experimental context, not only for quantum optimal control tasks, in order to impose finite energy bandwidth constraints on the control Hamiltonian [69,76].…”

Quantum technologies with optically interfaced solid-state spins

“…. Timedependent Hamiltonian engineering, such as optimal control154 and shortcuts to adiabacity 155 , could be extended for fast and robust gates despite densely spaced electron-nuclear energy levels. Furthermore, the convergence of quantum error correction and quantum sensing could improve sensitivity by extending qubit coherence regardless of the noise spectrum, in contrast to dynamical decoupling.…”

Time-optimal quantum transformations with bounded bandwidth

“…We allow the Hamiltonian governing the transformation to be time-dependent, but we assume that its energy bandwidth is uniformly bounded. Such an assumption is in many cases physically justified [8,9,10,11,12,13,14,15,16,17].…”