Manipulating quantum entanglement with atoms and photons in a cavity
TL;DR: The concept of entanglement plays an essential role in quantum physics as mentioned in this paper, and it is also essential to understand decoherence, the process accounting for the classical appearance of the macroscopic world.
Abstract: After they have interacted, quantum particles generally behave as a single nonseparable entangled system. The concept of entanglement plays an essential role in quantum physics. We have performed entanglement experiments with Rydberg atoms and microwave photons in a cavity and tested quantum mechanics in situations of increasing complexity. Entanglement resulted either from a resonant exchange of energy between atoms and the cavity field or from dispersive energy shifts affecting atoms and photons when they were not resonant. With two entangled particles (two atoms or one atom and a photon), we have realized new versions of the Einstein-Podolsky-Rosen situation. The detection of one particle projected the other, at a distance, in a correlated state. This process could be viewed as an elementary measurement, one particle being a ``meter'' measuring the other. We have performed a ``quantum nondemolition'' measurement of a single photon, which we detected repeatedly without destroying it. Entanglement is also essential to understand decoherence, the process accounting for the classical appearance of the macroscopic world. A mesoscopic superposition of states (``Schr\"odinger cat'') gets rapidly entangled with its environment, losing its quantum coherence. We have prepared a Schr\"odinger cat made of a few photons and studied the dynamics of its decoherence, in an experiment which constitutes a glimpse at the quantum/classical boundary. We have also investigated entanglement as a resource for the processing of quantum information. By using quantum two-state systems (qubits) instead of classical bits of information, one can perform logical operations exploiting quantum interferences and taking advantage of the properties of entanglement. Manipulating as qubits atoms and photons in a cavity, we have operated a quantum gate and applied it to the generation of a complex three-particle entangled state. We finally discuss the perspectives opened by these experiments for further fundamental studies.
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TL;DR: In this article, the basic aspects of entanglement including its characterization, detection, distillation, and quantification are discussed, and a basic role of entonglement in quantum communication within distant labs paradigm is discussed.
Abstract: All our former experience with application of quantum theory seems to say:
{\it what is predicted by quantum formalism must occur in laboratory} But the
essence of quantum formalism - entanglement, recognized by Einstein, Podolsky,
Rosen and Schr\"odinger - waited over 70 years to enter to laboratories as a
new resource as real as energy This holistic property of compound quantum systems, which involves
nonclassical correlations between subsystems, is a potential for many quantum
processes, including ``canonical'' ones: quantum cryptography, quantum
teleportation and dense coding However, it appeared that this new resource is
very complex and difficult to detect Being usually fragile to environment, it
is robust against conceptual and mathematical tools, the task of which is to
decipher its rich structure This article reviews basic aspects of entanglement including its
characterization, detection, distillation and quantifying In particular, the
authors discuss various manifestations of entanglement via Bell inequalities,
entropic inequalities, entanglement witnesses, quantum cryptography and point
out some interrelations They also discuss a basic role of entanglement in
quantum communication within distant labs paradigm and stress some
peculiarities such as irreversibility of entanglement manipulations including
its extremal form - bound entanglement phenomenon A basic role of entanglement
witnesses in detection of entanglement is emphasized
6,980 citations
TL;DR: In this article, it was shown that many of the symptoms of classicality can be induced in quantum systems by their environments, which leads to environment-induced superselection or einselection, a quantum process associated with selective loss of information.
Abstract: as quantum engineering. In the past two decades it has become increasingly clear that many (perhaps all) of the symptoms of classicality can be induced in quantum systems by their environments. Thus decoherence is caused by the interaction in which the environment in effect monitors certain observables of the system, destroying coherence between the pointer states corresponding to their eigenvalues. This leads to environment-induced superselection or einselection, a quantum process associated with selective loss of information. Einselected pointer states are stable. They can retain correlations with the rest of the universe in spite of the environment. Einselection enforces classicality by imposing an effective ban on the vast majority of the Hilbert space, eliminating especially the flagrantly nonlocal ''Schrodinger-cat states.'' The classical structure of phase space emerges from the quantum Hilbert space in the appropriate macroscopic limit. Combination of einselection with dynamics leads to the idealizations of a point and of a classical trajectory. In measurements, einselection replaces quantum entanglement between the apparatus and the measured system with the classical correlation. Only the preferred pointer observable of the apparatus can store information that has predictive power. When the measured quantum system is microscopic and isolated, this restriction on the predictive utility of its correlations with the macroscopic apparatus results in the effective ''collapse of the wave packet.'' The existential interpretation implied by einselection regards observers as open quantum systems, distinguished only by their ability to acquire, store, and process information. Spreading of the correlations with the effectively classical pointer states throughout the environment allows one to understand ''classical reality'' as a property based on the relatively objective existence of the einselected states. Effectively classical pointer states can be ''found out'' without being re-prepared, e.g, by intercepting the information already present in the environment. The redundancy of the records of pointer states in the environment (which can be thought of as their ''fitness'' in the Darwinian sense) is a measure of their classicality. A new symmetry appears in this setting. Environment-assisted invariance or envariance sheds new light on the nature of ignorance of the state of the system due to quantum correlations with the environment and leads to Born's rules and to reduced density matrices, ultimately justifying basic principles of the program of decoherence and einselection.
3,499 citations
TL;DR: It is shown that the strong coupling regime can be attained in a solid-state system, and the concept of circuit quantum electrodynamics opens many new possibilities for studying the strong interaction of light and matter.
Abstract: The interaction of matter and light is one of the fundamental processes occurring in nature, and its most elementary form is realized when a single atom interacts with a single photon. Reaching this regime has been a major focus of research in atomic physics and quantum optics1 for several decades and has generated the field of cavity quantum electrodynamics2,3. Here we perform an experiment in which a superconducting two-level system, playing the role of an artificial atom, is coupled to an on-chip cavity consisting of a superconducting transmission line resonator. We show that the strong coupling regime can be attained in a solid-state system, and we experimentally observe the coherent interaction of a superconducting two-level system with a single microwave photon. The concept of circuit quantum electrodynamics opens many new possibilities for studying the strong interaction of light and matter. This system can also be exploited for quantum information processing and quantum communication and may lead to new approaches for single photon generation and detection.
3,452 citations
Cites background from "Manipulating quantum entanglement w..."
...for several decades and has generated the field of cavity quantum electrodynamic...
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Proceedings Article•
01 Jan 2005TL;DR: In quantum optical devices, microcavities can coax atoms or quantum dots to emit spontaneous photons in a desired direction or can provide an environment where dissipative mechanisms such as spontaneous emission are overcome so that quantum entanglement of radiation and matter is possible.
Abstract: Microcavity physics and design will be reviewed. Following an overview of applications in quantum optics, communications and biosensing, recent advances in ultra-high-Q research will be presented.
2,857 citations
TL;DR: In this paper, a realizable architecture using one-dimensional transmission line resonators was proposed to reach the strong coupling limit of cavity quantum electrodynamics in superconducting electrical circuits.
Abstract: We propose a realizable architecture using one-dimensional transmission line resonators to reach the strong-coupling limit of cavity quantum electrodynamics in superconducting electrical circuits. The vacuum Rabi frequency for the coupling of cavity photons to quantized excitations of an adjacent electrical circuit (qubit) can easily exceed the damping rates of both the cavity and qubit. This architecture is attractive both as a macroscopic analog of atomic physics experiments and for quantum computing and control, since it provides strong inhibition of spontaneous emission, potentially leading to greatly enhanced qubit lifetimes, allows high-fidelity quantum nondemolition measurements of the state of multiple qubits, and has a natural mechanism for entanglement of qubits separated by centimeter distances. In addition it would allow production of microwave photon states of fundamental importance for quantum communication.
2,633 citations
References
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Book•
01 Jan 1994
TL;DR: Omnes as discussed by the authors examines a number of recent advances, which, combined with a consistent revision of the Copenhagen interpretation, lead to a consistent interpretation of quantum mechanics, which can fit all present experiments, to weed out unnecessary or questionable assumptions, and to assess the domain of validity where the older statements apply.
Abstract: The interpretation of quantum mechanics has been controversial since the introduction of quantum theory in the 1920s. Although the Copenhagen interpretation is commonly accepted, its usual formulation suffers from some serious drawbacks. Based mainly on Bohr's concepts, the formulation assumes an independent and essential validity of classical concepts running in parallel with quantum ones, and leaves open the possibility of their ultimate conflict. In this book, Roland Omnes examines a number of recent advances, which, combined, lead to a consistent revision of the Copenhagen interpretation. His aim is to show how this interpretation can fit all present experiments, to weed out unnecessary or questionable assumptions, and to assess the domain of validity where the older statements apply. The text offers a self-contained treatment of interpretation (in nonrelativistic physics) in a manner accessible to both physicists and students. Although some "hard" results are included, the concepts and mathematical developments are maintained at an undergraduate level. This book enables readers to check every step, apply the techniques to new problems and make sure that no paradox or obscurity
1,010 citations
"Manipulating quantum entanglement w..." refers background in this paper
...This fast relaxation process is called ‘‘decoherence’’ (Zurek, 1981, 1982, 1991; Caldeira and Leggett, 1983; Omnès, 1994)....
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TL;DR: The measurement of a quantum system is not consummated until irreversible processes have destroyed all phase coherence between different possible outcomes of that measurement as discussed by the authors, and it is inconsistent to assume that the wavefunction "collapses" before irreversibility sets in.
Abstract: The measurement of a quantum system is not consummated until irreversible processes have destroyed all phase coherence between different possible outcomes of that measurement. It is inconsistent to assume that the wavefunction ‘‘collapses’’ before irreversibility sets in.
327 citations
"Manipulating quantum entanglement w..." refers background in this paper
...Quantum nondemolition measurements have been proposed in the 1970s to improve the sensitivity of position or velocity measurements in gravitational wave detectors (Braginsky, Vorontsov, and Khalili, 1977; Braginsky and Khalili, 1992)....
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TL;DR: A discussion on this subject was held in the meeting of the Philosophy of Science Group on 8th December 1952, and I was asked to open it as discussed by the authors, but this was rather frustrated by Schrodinger's absence, due to serious illness.
Abstract: THE following pages are a reply to Erwin Schrodinger's article, ' Are There Quantum Jumps ? Parts I and II ' , published in August and November 1952, in this Journal. A discussion on this subject was to be held in the meeting of the Philosophy of Science Group on 8th December 1952, and I was asked to open it. I accepted this honour rather reluctantly, for I find it awkward to display in public a disagreement on a fundamental question with one of my best and oldest friends. Yet I had several motives for accepting the challenge : The first is my conviction that no discrepancy of opinion on scientific questions can shake our friendship. The second, that other good and old friends of the same standing as Schrodinger, such as Niels Bohr, Heisenberg and Pauli, share my opinion. My third, and the most important reason for entering into this discussion of Schrodinger's publication is that by its undeniable literary merits, the width of its historical and philosophical horizon, and the ingenious presentation of the arguments, it may have a confusing effect on the mind of those who, without being physicists, are interested in the general ideas of physio. The discussion on 8th December was rather frustrated by Schrodinger's absence, due to serious illness. I read my prepared introduction and answered questions. But this was, of course, not fair play to Schrodinger himself. Therefore I have to state my case in print. The following is a slightly enlarged version of my introduction to the discussion. As such, it covers not in the least all points made by Schrodinger, but only those which seemed to me suited for a debate amongst philosophers.
289 citations