Search results for "Quantum information"

2018

Abstract We show that a Wilson-type discretization of the Gross–Neveu model, a fermionic N -flavor quantum field theory displaying asymptotic freedom and chiral symmetry breaking, can serve as a playground to explore correlated symmetry-protected phases of matter using techniques borrowed from high-energy physics. A large- N study, both in the Hamiltonian and Euclidean formalisms, yields a phase diagram with trivial, topological, and symmetry-broken phases separated by critical lines that meet at a tri-critical point. We benchmark these predictions using tools from condensed matter and quantum information science, which show that the large- N method captures the essence of the phase diagram…

Control of nonlinear processes in two-photon excited rubidium vapour by resonant laser light

2019

Frequency up- and down-conversion in warm alkali vapours over a range of applied cw laser intensities has received much attention in recent years due to promising applications in the fields of remote detection, quantum information and computing, specifically in the implementation of correlated photon pairs, photon storage and quantum memory interface to name a few. The generation of directional laser-like blue and infrared light in alkali vapours has been extensively studied. However, important details of the interplay of parametric and nonparametric nonlinear processes, such as the four-wave mixing (FWM) and amplified spontaneous emission (ASE) responsible for the new field generation, are…

Teleportation-induced correlated quantum channels.

2009

Quantum teleportation of a n-qubit state performed using as entangled resource a general bipartite state of 2n qubits instead of n Bell states is equivalent to a correlated Pauli channel. This provides a new characterization of such channels in terms of many-body correlation functions of the teleporting media. Our model is then generalized to the Continuous Variable case. We show that this new representation provides a relatively simple method for determining whether a correlated quantum channel is able to reliably convey quantum messages by studying the entanglement properties of the teleportation mediating system.

Dynamical entanglement-transfer for quantum information networks

2004

A key element in the architecture of a quantum information processing network is a reliable physical interface between fields and qubits. We study a process of entanglement transfer engineering, where two remote qubits respectively interact with entangled two-mode continuous variable (CV) field. We quantify the entanglement induced in the qubit state at the expenses of the loss of entanglement in the CV system. We discuss the range of mixed entangled states which can be obtained with this set-up. Furthermore, we suggest a protocol to determine the residual entangling power of the light fields, inferring, thus, the entanglement left in the field modes which, after the interaction, are no lon…

Optomechanical to mechanical entanglement transformation

2008

We present a scheme for generating entanglement between two mechanical oscillators that have never interacted with each other by using an entanglement-swapping protocol. The system under study consists of a Michelson-Morley interferometer comprising mechanical systems embodied by two cantilevers. Each of them is coupled to a field mode via the radiation pressure mechanism. Entanglement between the two mechanical systems is set by measuring the output modes of the interferometer. We also propose a control mechanism for the amount of entanglement based on path-length difference between the two arms. © IOP Publishing Ltd and Deutsche Physikalische Gesellschaft.

Improving the coherence properties of solid-state spin ensembles via optimized dynamical decoupling

2016

In this work, we optimize a dynamical decoupling (DD) protocol to improve the spin coherence properties of a dense ensemble of nitrogen-vacancy (NV) centers in diamond. Using liquid nitrogen-based cooling and DD microwave pulses, we increase the transverse coherence time T2 from ∼ 0.7 ms up to ∼ 30 ms. We extend previous work of single-axis (Carr-Purcell-Meiboom-Gill) DD towards the preservation of arbitrary spin states. After performing a detailed analysis of pulse and detuning errors, we compare the performance of various DD protocols. We identify that the concatenated XY8 pulse sequences serves as the optimal control scheme for preserving an arbitrary spin state. Finally, we use the conc…

Quantum gate in the decoherence-free subspace of trapped ion qubits

2009

We propose a geometric phase gate in a decoherence-free subspace with trapped ions. The quantum information is encoded in the Zeeman sublevels of the ground-state and two physical qubits to make up one logical qubit with ultra long coherence time. Single- and two-qubit operations together with the transport and splitting of linear ion crystals allow for a robust and decoherence-free scalable quantum processor. For the ease of the phase gate realization we employ one Raman laser field on four ions simultaneously, i.e. no tight focus for addressing. The decoherence-free subspace is left neither during gate operations nor during the transport of quantum information.

A Three Dimensional Lattice of Ion Traps

2009

We propose an ion trap configuration such that individual traps can be stacked together in a three dimensional simple cubic arrangement. The isolated trap as well as the extended array of ion traps are characterized for different locations in the lattice, illustrating the robustness of the lattice of traps concept. Ease in the addressing of ions at each lattice site, individually or simultaneously, makes this system naturally suitable for a number of experiments. Application of this trap to precision spectroscopy, quantum information processing and the study of few particle interacting system are discussed.

Controlled long-range interactions between Rydberg atoms and ions

2016

We theoretically investigate trapped ions interacting with atoms that are coupled to Rydberg states. The strong polarizabilities of the Rydberg levels increases the interaction strength between atoms and ions by many orders of magnitude, as compared to the case of ground state atoms, and may be mediated over micrometers. We calculate that such interactions can be used to generate entanglement between an atom and the motion or internal state of an ion. Furthermore, the ion could be used as a bus for mediating spin-spin interactions between atomic spins in analogy to much employed techniques in ion trap quantum simulation. The proposed scheme comes with attractive features as it maps the bene…

Collective decoherence of cold atoms coupled to a Bose-Einstein condensate

2009

We examine the time evolution of cold atoms (impurities) interacting with an environment consisting of a degenerate bosonic quantum gas. The impurity atoms differ from the environment atoms, being of a different species. This allows one to superimpose two independent trapping potentials, each being effective only on one atomic kind, while transparent to the other. When the environment is homogeneous and the impurities are confined in a potential consisting of a set of double wells, the system can be described in terms of an effective spin-boson model, where the occupation of the left or right well of each site represents the two (pseudo)-spin states. The irreversible dynamics of such system…