Physical Review A

The convergence of quantum control strategies can be undermined by the presence of local minima in the optimization landscape. In this work, a bandwidth-limited optimal control algorithm is shown to offer a way to tailor this landscape, thus circumventing the problem.

We propose the continuous-variable quantum key distribution protocol based on the Gaussian modulation of a single quadrature of the coherent states of light, which is aimed to provide simplified implementation compared to the symmetrically modulated Gaussian coherent-state protocols. The protocol waives the necessity in one of the quadrature modulations and the corresponding channel transmittance…

When an atom is strongly coupled to a cavity, the two systems can exchange a single photon through a coherent Rabi oscillation. This process enables precise quantum-state engineering and manipulation of atoms and photons in a cavity, which play a central role in quantum information and measurement. Recently, a new regime of cavity QED was reached experimentally where the strength of the interacti…

One of the main applications of future quantum computers will be the\nsimulation of quantum models. While the evolution of a quantum state under a\nHamiltonian is straightforward (if sometimes expensive), using quantum\ncomputers to determine the ground state phase diagram of a quantum model and\nthe properties of its phases is more involved. Using the Hubbard model as a\nprototypical example, we…

High-resolution in situ imaging and manipulation of ultracold fermionic atoms in optical lattices are achieved experimentally for ${}^{40}$K with single-atom sensitivity. The tomographic imaging technique provides a promising tool to explore the physics of intriguing quantum many-body quantum phenomena in fermionic systems, such as unconventional superfluidity, transport and nonequilibrium dynami…

The appearance of so-called exceptional points in the complex spectra of non-Hermitian systems is often associated with phenomena that contradict our physical intuition. One example of particular interest is the state-exchange process predicted for an adiabatic encircling of an exceptional point. In this work we analyze this and related processes for the generic system of two coupled oscillator m…

In a variant of communication complexity tasks, two or more separated parties cooperate to compute a function of their local data, using a limited amount of communication. It is known that communication of quantum systems and shared entanglement can increase the probability for the parties to arrive at the correct value of the function, compared to classical resources. Here we show that quantum s…

We argue that a quantum annealer at very long annealing times is likely to experience a quasistatic evolution, returning a final population that is close to a Boltzmann distribution of the Hamiltonian at a single (freeze-out) point during the annealing. Such a system is expected to correlate with classical algorithms that return the same equilibrium distribution. These correlations do not mean th…

The analysis of photon scattering is a major challenge in the multiphoton regime. A framework based on a path-integral formalism provides a route to explore such dynamics, helping to investigate the quantum statistics of photons interacting with complex structures.

Molecular high-order harmonic generation from the ${{\mathrm{H}}_{2}}^{+}$ ion driven by spatial inhomogeneous fields consisting of the chirped pulse and a terahertz pulse has been theoretically investigated by numerically solving the non--Born-Oppenheimer time-dependent Schr\"odinger equation. It shows that with the introduction of the chirp as well as the spatial inhomogeneity of the pulse, not…

Nonadiabatic holonomic quantum computation has received increasing attention due to its robustness against control errors. However, all the previous schemes have to use at least two sequentially implemented gates to realize a general one-qubit gate. In this paper we put forward a scheme by which one can directly realize an arbitrary holonomic one-qubit gate with a single-shot implementation, avoi…

The availability of quantum annealing devices with hundreds of qubits has made the experimental demonstration of a quantum speedup for optimization problems a coveted, albeit elusive goal. Going beyond earlier studies of random Ising problems, here we introduce a method to construct a set of frustrated Ising-model optimization problems with tunable hardness. We study the performance of a D-Wave T…

We investigate quantum control of an oscillator mode off-resonantly coupled to an ancillary qubit. In the strong dispersive regime, we may drive the qubit conditioned on the number states of the oscillator, which, together with displacement operations, can achieve universal control of the oscillator. Based on our proof of universal control, we provide a straightforward recipe to perform arbitrary…

$S$-matrix theory of high-order harmonic generation (HHG) is generalized to multielectron atoms. In the multielectron case the harmonic power is expressed via a coherent sum of the time-dependent dipoles, while for the one-electron models a corresponding incoherent sum appears. This difference is important for the inert atomic gases having a $p$ ground state as used in a recent HHG experiment wit…

This paper defines the fidelity of recovery of a tripartite quantum state on systems $A,\phantom{\rule{0.16em}{0ex}}B$, and $C$ as a measure of how well one can recover the full state on all three systems if system $A$ is lost and a recovery operation is performed on system $C$ alone. The surprisal of the fidelity of recovery (its negative logarithm) is an information quantity which obeys nearly …

The logic Bell-state which encodes many physical qubits in a logic qubit has great application potential in the future quantum communication field, for it is robust to the decoherence in a noisy environment. In this paper, we propose a complete logic Bell-state analysis (LBSA) with the help of the auxiliary single atoms trapped in the low-quality cavity. We construct the parity-check measurement …

We establish a direct connection of quantum Markovianity of an open system to its classical counterpart by generalizing the criterion based on the information flow. Here the flow is characterized by the time evolution of Helstrom matrices, given by the weighted difference of statistical operators, under the action of the quantum dynamical map. It turns out that the introduced criterion is equival…

Quantum annealing provides a promising route for the development of quantum optimization devices, but the usefulness of such devices will be limited in part by the range of implementable problems as dictated by hardware constraints. To overcome constraints imposed by restricted connectivity between qubits, a larger set of interactions can be approximated using minor embedding techniques whereby s…

We propose the square of convex-roof extended negativity (SCREN) as a powerful candidate to characterize strong monogamy of multiparty quantum entanglement. We first provide a strong monogamy inequality of multiparty entanglement using SCREN and show that the tangle-based multiqubit strong-monogamy inequality can be rephrased by SCREN. We further show that the SCREN strong-monogamy inequality is …

Ergodicity, an essential property of a dynamical system for thermalization to occur, is found to be remarkably robust against disorder, which ultimately leads to many-body localization, and this robustness is predicted to be more significant in real-life-scale systems than in ultracold lattice experiments due to their limited size.