Exploring the Quantum

Haroche, S.; Raimond, Jean‐Michel

doi:10.1093/acprof:oso/9780198509141.001.0001

Cited by 1,431 publications

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“…In cavity quantum electrodynamics (QED) [1][2][3] , light-matter interaction is probed at its most fundamental level, where individual atoms are coupled to single photons stored in three-dimensional cavities. This unique possibility to experimentally explore the foundations of quantum physics has greatly evolved with the advent of circuit QED [4][5][6][7][8][9][10][11][12][13] , where on-chip superconducting qubits and oscillators play the roles of two-level atoms and cavities, respectively.…”

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confidence: 99%

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Circuit quantum electrodynamics in the ultrastrong-coupling regime

et al. 2010

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In cavity quantum electrodynamics (QED) 1-3 , light-matter interaction is probed at its most fundamental level, where individual atoms are coupled to single photons stored in three-dimensional cavities. This unique possibility to experimentally explore the foundations of quantum physics has greatly evolved with the advent of circuit QED 4-13 , where on-chip superconducting qubits and oscillators play the roles of two-level atoms and cavities, respectively. In the strong coupling limit, atom and cavity can exchange a photon frequently before coherence is lost. This important regime has been reached both in cavity and circuit QED, but the design flexibility and engineering potential of the latter allowed for increasing the ratio between the atom-cavity coupling rate g and the cavity transition frequency ωr above the percent level 8,14,15 . While these experiments are well described by the renowned Jaynes-Cummings model 16 , novel physics is expected when g reaches a considerable fraction of ωr. Promising steps towards this so-called ultrastrong coupling regime 17,18 have recently been taken in semiconductor structures 19,20 . Here, we report on the first experimental realization of a superconducting circuit QED system in the ultrastrong coupling limit and present direct evidence for the breakdown of the Jaynes-Cummings model. We reach remarkable normalized coupling rates g/ωr of up to 12 % by enhancing the inductive coupling of a flux qubit 21 to a transmission line resonator using the nonlinear inductance of a Josephson junction 22 . Our circuit extends the toolbox of quantum optics on a chip towards exciting explorations of the ultrastrong interaction between light and matter.In the strong coupling regime, the atom-cavity coupling rate g exceeds the dissipation rates κ and γ of both, cavity and atom, giving rise to coherent light-matter oscillations and superposition states. This regime was reached in various types of systems operating at different energy scales [1][2][3][23][24][25] . At microwave frequencies, strong coupling is feasible due to the enormous engineerability of superconducting circuit QED systems 4,5 . Here, small cavity mode volumes and large dipole moments of artificial atoms 26 enable coupling rates g of about 15 1 % of the cavity mode frequency ω r . Nevertheless, as in cavity QED, the quantum dynamics of these systems follows the Jaynes-Cummings model, which describes the coherent exchange of a single excitation between the atom and the cavity mode. Although the Hamiltonian of a realistic atom-cavity system contains so-called counterrotating terms allowing the simultaneous creation ior annihilation of an excitation in both atom and cavity mode, these terms can be safely neglected for small normalized coupling rates g/ω r . However, when g becomes a significant fraction of ω r , the counterrotating terms are expected to manifest, giving rise to exciting effects in QED.The ultrastrong coupling regime is difficult to reach in traditional quantum optics, but was recently realized in a solid-stat...

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“…This regime was reached in various types of systems operating at different energy scales [1][2][3][23][24][25] . At microwave frequencies, strong coupling is feasible due to the enormous engineerability of superconducting circuit QED systems 4,5 .…”

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Circuit quantum electrodynamics in the ultrastrong-coupling regime

et al. 2010

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“…More recently many experiments confirmed this viewpoint by realizing conditions that were similar to a measurement but involved only a few atoms or photons [3]: Von Neumann's standard description of a measurement as a creation of entanglement was found perfectly adequate [4], even when there was decoherence, and there was as predicted no glimpse of collapse in these experiments.…”

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confidence: 94%

Local Properties of Entanglement and Application to Collapse

Omnès

2013

Found Phys

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When a quantum system is macroscopic and becomes entangled with a microscopic one, this entanglement is not immediately total, but gradual and local. A study of this locality is the starting point of the present work and shows unexpected and detailed properties in the generation and propagation of entanglement between a measuring apparatus and a microscopic measured system. Of special importance is the propagation of entanglement in nonlinear waves with a finite velocity. When applied to the entanglement between a macroscopic system and its environment, this study yields also new results about the resulting disordered state. Finally, a mechanism of wave function collapse is proposed as an effect of perturbation in the growth of local entanglement between a measuring system and the measured one by waves of entanglement with the environment.Keywords: entanglement, kinetic physics, decoherence, wave function collapse _________ This is a revised version of arxiv.org.quant.phys.13093472, partly rewritten for clarity and with two previous key assumptions reconsidered, page 20: II as still convenient but unnecessary and III as being now proved.It became clear early in the theory of quantum measurements -particularly in Schrödinger's works [1, 2]-that entanglement is the stumbling block forbidding emergence of a unique datum in a measurement. More recently many experiments confirmed this viewpoint by realizing conditions that were similar to a measurement but involved only a few atoms or photons [3]: Von Neumann's standard description of a measurement as a creation of entanglement was found perfectly adequate [4], even when there was decoherence, and there was as predicted no glimpse of collapse in these experiments.An obvious consequence is that collapse, or the emergence of reality, is essentially a macroscopic phenomenon. This conclusion was drawn particularly in the theory of spontaneous collapse at a small but macroscopic scale by Ghirardi, Rimini and Weber [5], but in a form requiring modification in the quantum principles: The existence of a collapse effect with universal range and universal rate was added to these principles, the essential role of this effect being to break down the deadly obstruction from entanglement.But one may also wonder whether entanglement is so total and rigid that a new principle is needed to break it. Is it impossible to look at it more ordinarily as a physical phenomenon needing time for its growth and space for its expansion, rather than remaining an absolute mathematical property of wave functions? This question can stand in some sense as the starting point of the present work.When describing the nature of entanglement, Schrödinger considered an example where two quantum systems A and B, initially independent, begin to interact at some time zero and separate again after some more time [2]. Both systems are initially in a pure state but, although this is still true of the compound system AB after their interaction, it is not

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“…The explicit mapping is provided by the relation σ (t) ↔ Nt. Further insight into the meaning of the involved parameters may be gained using a short-time detuning-independent approximation for σ (t) 1 2 λγ t 2 .…”

Section: Systemmentioning

confidence: 99%

“…Environment-induced decoherence is the prevailing explanation for the loss of nonclassicality of an open quantum system, being responsible for the relaxation of the system to a statistical mixture of classical-like states [1][2][3]. In this framework, a nonzero-temperature environment is usually described in terms of a quantized ensemble of simple physical systems, e.g., harmonic oscillators or spins, spanning a wide frequency range and interacting with the quantum system of interest through a suitable interaction Hamiltonian.…”

Section: Introductionmentioning

confidence: 99%

Collapse and revival of quantum coherence for a harmonic oscillator interacting with a classical fluctuating environment

et al. 2015

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We address the dynamics of nonclassicality for a quantum system interacting with a noisy fluctuating environment described by a classical stochastic field. As a paradigmatic example, we consider a harmonic oscillator initially prepared in a maximally nonclassical state, e.g., a Fock number state or a Schrödinger-cat-like state, and then coupled to either a resonant or a nonresonant external field. Stochastic modeling allows us to describe the decoherence dynamics without resorting to approximated quantum master equations and to introduce non-Markovian effects in a controlled way. A detailed comparison among different nonclassicality criteria and a thorough analysis of the decoherence time reveal a rich phenomenology whose main features may be summarized as follows: (i) Classical memory effects increase the survival time of quantum coherence and (ii) a detuning between the natural frequency of the system and the central frequency of the classical field induces revivals of quantum coherence.

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Exploring the Quantum

Cited by 1,431 publications

References 0 publications

Circuit quantum electrodynamics in the ultrastrong-coupling regime

Circuit quantum electrodynamics in the ultrastrong-coupling regime

Local Properties of Entanglement and Application to Collapse

Collapse and revival of quantum coherence for a harmonic oscillator interacting with a classical fluctuating environment

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