14 research outputs found
Quantum Speed Limit and Optimal Control of Many-Boson Dynamics
We extend the concept of quantum speed limit -- the minimal time needed to
perform a driven evolution -- to complex interacting many-body systems. We
investigate a prototypical many-body system, a bosonic Josephson junction, at
increasing levels of complexity: (a) within the two-mode approximation
{corresponding to} a nonlinear two-level system, (b) at the mean-field level by
solving the nonlinear Gross-Pitaevskii equation in a double well potential, and
(c) at an exact many-body level by solving the time-dependent many-body
Schr\"odinger equation. We propose a control protocol to transfer atoms from
the ground state of a well to the ground state of the neighbouring well.
Furthermore, we show that the detrimental effects of the inter-particle
repulsion can be eliminated by means of a compensating control pulse, yielding,
quite surprisingly, an enhancement of the transfer speed because of the
particle interaction -- in contrast to the self-trapping scenario. Finally, we
perform numerical optimisations of both the nonlinear and the (exact) many-body
quantum dynamics in order to further enhance the transfer efficiency close to
the quantum speed limit.Comment: 5 pages, 3 figures, and supplemental material (4 pages 1 figure
Autonomous Calibration of Single Spin Qubit Operations
Fully autonomous precise control of qubits is crucial for quantum information
processing, quantum communication, and quantum sensing applications. It
requires minimal human intervention on the ability to model, to predict and to
anticipate the quantum dynamics [1,2], as well as to precisely control and
calibrate single qubit operations. Here, we demonstrate single qubit autonomous
calibrations via closed-loop optimisations of electron spin quantum operations
in diamond. The operations are examined by quantum state and process
tomographic measurements at room temperature, and their performances against
systematic errors are iteratively rectified by an optimal pulse engineering
algorithm. We achieve an autonomous calibrated fidelity up to 1.00 on a time
scale of minutes for a spin population inversion and up to 0.98 on a time scale
of hours for a Hadamard gate within the experimental error of 2%. These results
manifest a full potential for versatile quantum nanotechnologies.Comment: 9 pages, 5 figure
Bayesian-based hybrid method for rapid optimization of NV center sensors
NV center is one of the most promising platforms in the field of quantum
sensing. Magnetometry based on NV center, especially, has achieved a concrete
development in regions of biomedicine and medical diagnostics. Improving the
sensitivity of NV center sensor under wide inhomogeneous broadening and filed
amplitude drift is one crucial issue of continuous concern, which relies on the
coherent control of NV center with higher average fidelity. Quantum optimal
control (QOC) methods provide access to this target, nevertheless the high time
consumption of current methods due to the large number of needful sample points
as well as the complexity of the parameter space has hindered their usability.
In this paper we propose the Bayesian estimation phase-modulated (B-PM) method
to tackle this problem. In the case of state transforming of NV center
ensemble, the B-PM method reduces the time consumption by more than
compared to the conventional standard Fourier base (SFB) method while
increasing the average fidelity from to . In AC magnetometry
scenery, the optimized control pulse given by B-PM method achieves a eight-fold
extension of the coherence time compared to rectangular pulse.
Similar application can be made in other sensing situations. As a general
algorithm, the B-PM method can be further extended to open- and closed-loop
optimization of complex systems based on a variety of quantum platforms
Rapid transform optimisation strategy for decoherence-protected quantum register in diamond
Decoherence-protected spins associated with nitrogen-vacancy color centers in
diamond possess remarkable long coherence time, which make them one of the most
promising and robust quantum registers. The current demand is to explore
practical rapid control strategies for preparing and manipulating the such
register. Our work provides all-microwave control strategies optimized using
multiple optimization methods to significantly reduce the processing time by
with a set of smooth near-zero-endpoints control fields that are shown
to be experimentally realizable. Furthermore, we optimize and analyze the
robustness of these strategies under frequency and amplitude imperfections of
the control fields, during which process we use only samples to give a
fair estimation of the robustness map with pixels. Overall, we provide a
ready-to-implement recipe to facilitate high-performance information processing
via decoherence-protected quantum register for future quantum technology
applications.Comment: 8 pages, 5 figure
Precise ultra fast single qubit control using optimal control pulses
Ultra fast and accurate quantum operations are required in many modern
scientific areas - for instance quantum information, quantum metrology and
magnetometry. However the accuracy is limited if the Rabi frequency is
comparable with the transition frequency due to the breakdown of the rotating
wave approximation (RWA). Here we report the experimental implementation of a
method based on optimal control theory, which does not suffer these
restrictions. We realised the most commonly used quantum gates - the Hadamard
(\pi/2 pulse) and NOT (\pi pulse) gates with fidelities
( and
), in an excellent agreement with the
theoretical predictions ( and
). Moreover, we demonstrate magnetic
resonance experiments both in the rotating and lab frames and we can
deliberately "switch" between these two frames. Since our technique is general,
it could find a wide application in magnetic resonance, quantum computing,
quantum optics and broadband magnetometry.Comment: New, updated version of the manuscript with supplementary informatio
One decade of quantum optimal control in the chopped random basis
The Chopped RAndom Basis (CRAB) ansatz for quantum optimal control has been proven to be a versatile tool to enable quantum technology applications, quantum computing, quantum simulation, quantum sensing, and quantum communication. Its capability to encompass experimental constraints -- while maintaining an access to the usually trap-free control landscape -- and to switch from open-loop to closed-loop optimization (including with remote access -- or RedCRAB) is contributing to the development of quantum technology on many different physical platforms. In this review article we present the development, the theoretical basis and the toolbox for this optimization algorithm, as well as an overview of the broad range of different theoretical and experimental applications that exploit this powerful technique
One decade of quantum optimal control in the chopped random basis
The chopped random basis (CRAB) ansatz for quantum optimal control has been proven to be a versatile tool to enable quantum technology applications such as quantum computing, quantum simulation, quantum sensing, and quantum communication. Its capability toencompass experimental constraints—while maintaining an access to the usually trap-free control landscape—and to switch from open-loop to closed-loop optimization (including with remote access—or RedCRAB) is contributing to the development of quantum technology on many different physical platforms. In this review article we present the development, the theoretical basis and the toolbox for this optimization algorithm, as well as an overview of the broad range of different theoretical and experimental applications that exploit this powerfultechnique
Optimal quantum optical control of spin in diamond
The nitrogen-vacancy (NV) center spin represents an appealing candidate for
quantum information processing. Besides the widely used microwave control, its
coherent manipulation may also be achieved using laser as mediated by the
excited energy levels. Nevertheless, the multiple levels of the excited state
of NV center spin make the coherent transition process become complex and may
affect the fidelity of coherent manipulation. Here, we adopt the strategy of
optimal quantum control to accelerate coherent state transfer in the ground
state manifold of NV center spin using laser. The results demonstrate improved
performance in both the speed and the fidelity of coherent state transfer which
will be useful for optical control of NV center spin in diamond