22 research outputs found
Reconstruction of non-classical cavity field states with snapshots of their decoherence
The state of a microscopic system encodes its complete quantum description, from which the probabilities of all measurement outcomes are inferred. Being a statistical concept, the state cannot be obtained from a single system realization, but can instea
Ultrahigh finesse Fabry-Perot superconducting resonator
We have built a microwave Fabry-Perot resonator made of diamond-machined
copper mirrors coated with superconducting niobium. Its damping time (Tc = 130
ms at 51 GHz and 0.8 K) corresponds to a finesse of 4.6 x 109, the
highest ever reached for a Fabry-Perot in any frequency range. This result
opens novel perspectives for quantum information, decoherence and non-locality
studies
Photon-number discrimination without a photon counter and its application to reconstructing non-Gaussian states
The nonlinearity of a conditional photon-counting measurement can be used to "de-Gaussify" a Gaussian state of light. Here we present and experimentally demonstrate a technique for photon-number resolution using only homodyne detection. We then apply this technique to inform a conditional measurement, unambiguously reconstructing the statistics of the non-Gaussian one- and two-photon-subtracted squeezed vacuum states. Although our photon-number measurement relies on ensemble averages and cannot be used to prepare non-Gaussian states of light, its high efficiency, photon-number- resolving capabilities, and compatibility with the telecommunications band make it suitable for quantum-information tasks relying on the outcomes of mean values
Electromagnetically induced transparency and fourwave mixing in a cold atomic ensemble with large optical depth
We report on the delay of optical pulses using electromagnetically induced transparency (EIT) in an ensemble of cold atoms with an optical depth exceeding 500. To identify the regimes in which four-wave mixing (4WM) impacts on EIT behaviour, we conduct the experiment in both 85Rb and 87Rb. Comparison with theory shows excellent agreement in both isotopes. In 87Rb negligible 4WM was observed and we obtained one pulse-width of delay with 50% efficiency. In 85Rb 4WM contributes to the output. In this regime we achieve a delay-bandwidth product of 3.7 at 50% ef ficiency, allowing temporally multimode delay, which we demonstrate by compressing two pulses into the memory medium
Rotational modes in molecular magnets with antiferromagnetic Heisenberg exchange
In an effort to understand the low temperature behavior of recently
synthesized molecular magnets we present numerical evidence for the existence
of a rotational band in systems of quantum spins interacting with
nearest-neighbor antiferromagnetic Heisenberg exchange. While this result has
previously been noted for ring arrays with an even number of spin sites, we
find that it also applies for rings with an odd number of sites as well as for
all of the polytope configurations we have investigated (tetrahedron, cube,
octahedron, icosahedron, triangular prism, and axially truncated icosahedron).
It is demonstrated how the rotational band levels can in many cases be
accurately predicted using the underlying sublattice structure of the spin
array. We illustrate how the characteristics of the rotational band can provide
valuable estimates for the low temperature magnetic susceptibility.Comment: 14 pages, 7 figures, to be published in Phys. Rev.
Quantum jumps of light recording the birth and death of a photon in a cavity
A microscopic system under continuous observation exhibits at random times
sudden jumps between its states. The detection of this essential quantum
feature requires a quantum non-demolition (QND) measurement repeated many times
during the system evolution. Quantum jumps of trapped massive particles
(electrons, ions or molecules) have been observed, which is not the case of the
jumps of light quanta. Usual photodetectors absorb light and are thus unable to
detect the same photon twice. They must be replaced by a transparent counter
'seeing' photons without destroying them3. Moreover, the light has to be stored
over a duration much longer than the QND detection time. We have fulfilled
these challenging conditions and observed photon number quantum jumps.
Microwave photons are stored in a superconducting cavity for times in the
second range. They are repeatedly probed by a stream of non-absorbing atoms. An
atom interferometer measures the atomic dipole phase shift induced by the
non-resonant cavity field, so that the final atom state reveals directly the
presence of a single photon in the cavity. Sequences of hundreds of atoms
highly correlated in the same state, are interrupted by sudden
state-switchings. These telegraphic signals record, for the first time, the
birth, life and death of individual photons. Applying a similar QND procedure
to mesoscopic fields with tens of photons opens new perspectives for the
exploration of the quantum to classical boundary
Mesures QND en electrodynamique quantique en cavite : production et decoherence d'etats de Fock ; effet Zenon quantique
We have implemented a Quantum Non Demolition measurement of the photon number of a field stored in a cavity of damping time T=0.13s. We send circular Rydberg atoms in the cavity. A dispersive interaction shifts the atomic frequency linearly in the photon number. This light-shift is detected by atomic Ramsey interferometry. The cavity damping time is long enough to observe the quantum jumps induced by relaxation. By a statistical analysis of the different trajectories, we carry out a partial tomography of this process responsible for the decoherence of the Fock states |n> within a time T/n. The projection of the initially coherent field onto a Fock state during a measurement completely blurs the field phase simultaneously. This back-action can freeze the coherent growth of the field by quantum Zeno effect.Nous avons realise une mesure Quantiques Non Destructives du nombre de photons d'un champ piege dans une cavite de temps d'amortissement T=0,13s. Nous envoyons des atomes de Rydberg circulaires a travers la cavite ou une interaction dispersive deplace leur frequence propre proportionnellement au nombre de photons. Ce deplacement lumineux est detecte par interferometrie atomique de Ramsey. Le temps d'amortissement du champ est suffisamment long pour permettre d'observer les sauts quantiques du nombre de photons dus a la relaxation. L'analyse statistique des differentes trajectoires permet de realiser une tomographie partielle de ce processus responsable de la decoherence des etats de Fock |n> en un temps T/n. La projection d'un champ initialement coherent sur un etat de Fock lors de la mesure s'accompagne d'une dispersion totale de sa phase. Cette action en retour est utilisee pour geler la croissance coherente du champ par effet Zenon quantique
Mesures QND en électrodynamique quantique en cavité (production et décohérence d'états de Fock)
PARIS-BIUSJ-Thèses (751052125) / SudocPARIS-BIUSJ-Physique recherche (751052113) / SudocSudocFranceF