Review article: “Open-System Dynamics of Entanglement”

Leandro Aolita (former PhD student at IF-UFRJ and now Marie Curie fellow at Freie Universität Berlin), Luiz Davidovich (IF-URFJ), and I (Fernando) (qig@CBPF), finally put online a preliminary version of our review paper on the dynamics of entanglement in open quantum systems. You can find the review at arXiv:1402.3713 .

It took us six years of intensive work to get this done. It was almost painful, but we are really happy with the outcome! The preliminary version of the review is 76 pages long, contains 32 pictures, and 500 citations! And it’s still growing!! We tried to be very careful in not only to compile a bunch of interesting results, but also to give the necessary tools and insights as to make the results clear. We hope that it’s going to be useful and accessible both for experts and beginners, theoreticians and experimentalists. Comments are welcome!

Without further ado:

Title: Open-System Dynamics of Entanglement

Authors: Leandro Aolita, Fernando de Melo, Luiz Davidovich

Available at: arXiv:1402.3713

Abstract: “One of the greatest challenges in the fields of quantum information processing and quantum technologies is the detailed coherent control over each and all of the constituents of quantum systems with an ever increasing number of particles. Within this endeavor, the harnessing of many-body entanglement against the detrimental effects of the environment is a major and pressing issue. Besides being an important concept from a fundamental standpoint, entanglement has been recognised as a crucial resource for quantum speed-ups or performance enhancements over classical methods. Understanding and controlling many-body entanglement in open systems may have strong implications in quantum computing, quantum simulations of many-body systems, secure quantum communication or cryptography, quantum metrology, our understanding of the quantum-to-classical transition, and other important questions of quantum foundations.

In this paper we present an overview of recent theoretical and experimental efforts to underpin the dynamics of entanglement under the influence of noise. Entanglement is thus taken as a dynamic quantity on its own, and we survey how it evolves due to the unavoidable interaction of the entangled system with its surroundings. We analyse several scenarios, corresponding to different families of states and environments, which render a very rich diversity of dynamical behaviors.

In contrast to single-particle quantities, like populations and coherences, which typically vanish only asymptotically in time, entanglement may disappear at a finite time. In addition, important classes of entanglement display an exponential decay with the number of particles when subject to local noise, which poses yet another threat to the already-challenging scaling of quantum technologies. Other classes, however, turn out to be extremely robust against local noise. Theoretical results and recent experiments regarding the difference between local and global decoherence are summarized. Control and robustness-enhancement techniques, scaling laws, statistical and geometrical aspects of multipartite-entanglement decay are also reviewed; all in order to give a broad picture of entanglement dynamics in open quantum systems addressed to both theorists and experimentalists inside and outside the field of quantum information.”



QM Talks@CBPF: Slides online!


the last two talks at our QM Talks@CBPF were just great!

Process of parameter estimation

Bruno showed us how to obtain the minimum error in the estimation of a parameter when the dynamical process that the probe undergoes, which depends on the parameter we want to estimate, is a noisy quantum one. This was an open question for almost 30 years! Congratulations to Bruno, Ruynet, and Luiz for a great series of works in quantum metrology!
Here are the slides for Bruno’s talk: Bruno’s slides

Pablo’s talk concerned the theoretical description of the beautiful cQED experiments carried out in the group of Luis Orozco (Maryland).

Experimental setup - cQED group@Maryland

In his very didactic talk, Pablo showed us how to theoretically describe the quantum beats that were measured by Orozco’s team via the two-point correlation function. More than that, he also showed us that by post-selecting some states that leak out the cavity they can suppress the decoherence in the quantum beats. And this is not only a proposal, they measured it!
The slides for Pablo’s talk are here: Pablo’s slides

Thanks again for Bruno and Pablo for the great talks!

…And stay tuned for the next QM Talks@CBPF!

QM Talks@CBPF: Pablo B. Blostein (UNAM) — 24.07, 16h

Continuing with our series of seminars, we have Pablo B. Blostein from Universidad Nacional Autónoma de México (UNAM). He’ll show us how to control decoherence by postselection. Be sure to be there! Details below.

Notice the time change! Our QM Talks@CBPF are now 16h!!

Speaker: Pablo B. Blostein (IIMAS-UNAM)
Title: Using postselection to control ground state quantum beats in Cavity QED
Coordinates: 24.07, 16h @ CBPF Seminar room 601C
Abstract: Ground state quantum beats observed in the second order intensity correlation from a continuously driven atomic ensemble inside a two mode optical cavity are subject to a frequency shift and decoherence. While driving the cavity with light of linear polarization (π transitions) the second order autocorrelation function is measured in the undriven mode (orthogonal polarization): a first photon detection prepares a superposition of atomic ground state Zeeman sublevels and the second measures the ground state beats. Between these two detections, the atoms can become excited and return to the ground state, emitting most of the photons into modes other than the cavity modes. Depending on the drive strength this process can happen several times. Each time there is a relative phase advance between the Zeeman sublevels. The information of this phase advance and its associated decoherence is then leaked into the modes that are not the cavity modes, which form the environment. It is possible to get information about the number of photons leaked into the environment by monitoring the driven mode. Here we propose a scheme to manipulate the loss of amplitude of the beats (decoherence) and the beat frequency shift, by postselecting on the basis of information gathered through measurement of the driven cavity mode. This proposal is a new strategy compared with controlling the decoherence and light shift through turning off the driven field.