High-fidelity controlled-phase gates based on the Rydberg blockade have been studied and their robustness with respect to noise experimental inaccuracies in pulse timings amplitudes using both analytic numerically optimized pulses investigated.

With recent improvements in coherence times, superconducting transmon qubits have become a promising platform for quantum computing. They can be flexibly engineered over wide range of parameters, but also require us to identify an efficient operating regime. Using state-of-the-art optimal control techniques, we exhaustively explore the landscape creation and removal entanglement design parameters. We region outside usually considered strongly dispersive regime, where multiple sources...

We study optimal quantum control of the dynamics trapped Bose-Einstein condensates: The targets are to split a condensate, residing initially in single well, into double without inducing excitation, and excite condensate from ground state first-excited well. is described mean-field approximation Gross-Pitaevskii equation. compare two optimization approaches terms their performance ease use; namely, gradient-ascent pulse engineering (GRAPE) Krotov's method. Both derived variational principle...

Optimal control theory is a powerful tool for improving figures of merit in quantum information tasks. Finding the solution to any optimal problem via numerical optimization depends crucially on choice functional. Here, we derive functional that targets full set two-qubit perfect entanglers, gates capable creating maximally-entangled state out some initial product state. The easily-computable local invariants and uniquely determines when gate evolves into entangler. Optimization with our...

The robustness of an atomic fountain interferometer with respect to variations in the initial velocity atoms and deviations from optimal pulse amplitude is examined. We numerically simulate dynamics momentum space a maximum separation 20ℏk map out expected signal contrast depending on variance distribution value laser field amplitude. show that excitation scheme based rapid adiabatic passage significantly enhances contrast, compared commonly used consisting series π/2 π pulses. demonstrate...

The accurate transport of an ion over macroscopic distances represents a challenging control problem due to the different length and time scales that enter experimental limitations on controls need be accounted for. Here, we investigate performance techniques for in state-of-the-art segmented miniaturized traps. We employ numerical optimization classical trajectories quantum wavepacket propagation as well analytical solutions derived from invariant based inverse engineering geometric optimal...

The difficulty of an optimization task in quantum information science depends on the proper mathematical expression physical target. Here we demonstrate power functionals targeting arbitrary perfect two-qubit entangler, which allow generation a maximally entangled state from some initial product state. We show for two platforms current interest, i.e., nitrogen vacancy centers diamond and superconducting Josephson junctions, that entangler can be reached faster with higher fidelity than both...

Optimal control theory is a powerful tool for solving problems in quantum mechanics, ranging from the of chemical reactions to implementation gates computer. Gradient-based optimization methods are able find high fidelity controls, but require considerable numerical effort and often yield highly complex solutions. We propose here employ two-stage scheme significantly speed up convergence achieve simpler controls. The initially parametrized using only few free parameters, such that this...

We develop a framework of "semi-automatic differentiation" that combines existing gradient-based methods quantum optimal control with automatic differentiation. The approach allows to optimize practically any computable functional and is implemented in two open source Julia packages, GRAPE.jl Krotov.jl, part the QuantumControl.jl framework. Our method based on formally rewriting optimization terms propagated states, overlaps target or gates. An analytical application chain rule then separate...

Considering the unique energy level structure of one-axis twisting Hamiltonian in combination with standard rotations, we propose implementation a rapid adiabatic passage scheme on Dicke state basis. The method permits to drive states many-atom system into entangled maximum quantum Fisher information. designed allow us overcome classical limit phase sensitivity metrology and sensing. We show how generate superpositions states, which maximize metrological gain for Ramsey interferometric...

We discuss the production of ultracold molecules in their electronic ground state by photoassociation employing electronically excited states with ion-pair character and strong spin-orbit interaction. A short laser pulse drives a nonresonant three-photon transition for alkali-metal atoms colliding lowest triplet state. The excited-state wave packet is transferred to second pulse, driving resonant two-photon transition. After analyzing matrix elements governing stabilization step, we...

We study controlled phasegates for ultracold atoms in an optical potential. A shaped laser pulse drives transitions between the ground and electronically excited states where are subject to a long-range 1/R3 interaction. fully account this interaction use optimal control theory calculate shapes. This allows us determine minimum duration, respectively, gate time T that is required obtain high fidelity. accurately analyse speed limiting factors, we find be limited either by strength state or...

We present a new open-source Python package, krotov, implementing the quantum optimal control method of that name. It allows to determine time-dependent external fields for wide range problems, including state-to-state transfer, gate implementation and optimization towards an arbitrary perfect entangler. Krotov's compares other gradient-based methods such as gradient-ascent guarantees monotonic convergence approximately time-continuous fields. The user-friendly interface combination with...

We propose a scheme for the generation of optimal squeezed states Ramsey interferometry. The consists an alternating series one-axis twisting pulses and rotations, both which are straightforward to implement experimentally. resulting show metrological gain proportional Heisenberg limit. demonstrate that scaling is maintained even when placing constraints on amplitude implementing taking into account realistic losses due photon scattering.

We show that optimizing a quantum gate for an open system requires the time evolution of only three states irrespective dimension Hilbert space. This represents significant reduction in computational resources compared to complete basis Liouville space is commonly believed necessary this task. The based on two observations: target not general dynamical map but unitary operation; and properly chosen sufficient distinguish any unitaries. illustrate optimization employing reduced set controlled...

We present possible design concepts for a tractor atom interferometer (TAI) based on three-dimensional confinement and transport of ultracold atoms. The reduces device size wave-packet dispersion, enables arbitrary holding times, facilitates control to create complex trajectories that allow optimization cancel unwanted sensitivity, fast splitting recombination, suppression detrimental nonadiabatic excitation. Thus, the allows further advancement compact, high-sensitivity, quantum sensing...

We investigate the possible realization of an ultracold-atom rotation sensor that is based on recently proposed tractor atom interferometry (TAI). An experimental design includes generation a Laguerre–Gaussian-beam-based “pinwheel” optical lattice and multi-loop interferometric cycles discussed. Numerical simulations system demonstrate TAI sensitivity comparable to contemporary matter-wave interferometers. analyze regime sensors in which nonadiabatic effects may hinder system's performance....

The wave-function Monte-Carlo method, also referred to as the use of "quantum-jump trajectories", allows efficient simulation open systems by independently tracking evolution many pure-state "trajectories". This method is ideally suited modern, highly parallel computers. Here we show that Krotov's numerical optimal control, unlike others, can be modified in a simple way, so it becomes fully pure states without losing its effectiveness. provides for finding control protocols quantum and...

We present an analysis of the robustness existing analytic schemes for implementation atomic fountain interferometer, and develop concepts improving this through use optimal control theory. For interferometer operating in Raman regime, we consider that manipulates momentum states with a series Rabi pulses, analyze how robust population dynamics are respect to variations effective pulse amplitude seen by atoms clouds, initial velocity relative rest frame. then show using rapid adiabatic...

Implementation of logical entangling gates is an important step towards realizing a quantum computer. We use gradient-based optimization approach to find single-qubit rotations which can be interleaved between applications noisy nonlocal gate dramatically suppress arbitrary errors, while steering the evolution operator perfectly subset SU(4) gates. The modularity allows for application any two-qubit system, regardless Hamiltonian or details experimental implementation. This effective both...