Nondestructive Rydberg Atom Counting with Mesoscopic Fields in a Cavity

Collège de France, Lutetia Parisorum, Île-de-France, France
Physical Review Letters (Impact Factor: 7.51). 04/2005; 94(11):113601. DOI: 10.1103/PhysRevLett.94.113601
Source: PubMed


We present an efficient, state-selective, nondemolition atom-counting procedure based on the dispersive interaction of a sample of circular Rydberg atoms with a mesoscopic field contained in a high-quality superconducting cavity. The state-dependent atomic index of refraction, proportional to the atom number, shifts the classical field phase. A homodyne procedure translates the information from the phase to the intensity. The final field intensity is readout by a mesoscopic atomic sample. This method opens promising routes for quantum information processing and nonclassical state generation with Rydberg atoms.

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Available from: A. Auffèves, May 12, 2014
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    • "Real quantum measurements almost always cause a much stronger back action than required by the laws of quantum mechanics. Quantum non-demolition (QND) measurements have been devised [1] [2] [3] [4] [5] [6] such that the additional back action is kept entirely within observables other than the one being measured. However, this back action to other observables often also imposes constraints. "
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    ABSTRACT: Real quantum measurements almost always cause a much stronger back action than required by the laws of quantum mechanics. In particular, free-space optical detection methods for single atoms and ions such as the shelving technique, though being among the most sensitive detection methods in quantum physics, inevitably require spontaneous scattering, even in the dispersive regime. This causes heating, a limitation for atom-based quantum information processing where it obviates straightforward reuse of the qubit. No such energy exchange is required by quantum mechanics. Here we experimentally demonstrate optical detection of an atomic qubit with significantly less than one spontaneous scattering event. We measure transmission and reflection of an optical cavity containing the atom. In addition to the qubit detection itself, we quantitatively measure how much spontaneous scattering has occurred. This allows us to relate the information gained to the amount of spontaneous emission, and we obtain a detection error below 10% while scattering less than 0.2 photons on average. Furthermore, we perform a quantum Zeno type experiment to quantify the measurement back action and find that every incident photon leads to an almost complete state collapse. Together, these results constitute a full experimental characterization of a quantum measurement in the "energy exchange-free" regime below a single spontaneous emission event. Besides its fundamental interest, this means significant simplification for proposed neutral-atom quantum computation schemes and may enable sensitive detection of molecules and atoms lacking closed transitions.
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    ABSTRACT: Tese (doutorado)—Universidade de Brasília, Instituto de Física, 2006. Neste trabalho investigamos a preparaçao de estados nao-classicos do campo eletromagnetico quantizado, confinado em cavidade microonda, ou em modo viajante; a saber: superposiçoes circulares de estados coerentes e de estados coerentes comprimidos; superposiçoes de estados de fase de Pegg-Barnett e estados de Fock arbitrarios. Mostramos que, para convenientes escolhas de parametros, a superposiçao circular de estados coerentes permitem obter estados de Fock do tipo |2N>, com N = 1, 2, 3, . . ., incluindo suas superposiçoes A|2N>+B|2N+1>. Enquanto que a superposiçao circular de estados coerentes comprimidos possibilita obter umaclasse mais ampla de estados de Fock, a saber,| k2N>, k = 1, 2, 3, .... Apresentamos também propostas de medida indireta da funçao de Wigner e de dispositivo que implementa a operaçao de deslocamento condicional para estados em modos viajantes, apropriado para gerar superposiçoes do tipo |Ã> ± ^D (alfa) | Ã>, incluindo interessantes casos particulares. _________________________________________________________________________________ ABSTRACT In this work we investigate the preparation of the nonclassical states of the quantized electromagnetic field, for trapped modes in microwave cavity and traveling modes, namely: circular superpositions of coherent states and squeezed coherent states; superpositions of (Pegg- Barnett) phase states and arbitrary Fock states. The circular superpositions of coherent states allow us to get Fock states of the kind |2Ni, with N = 1, 2, 3, . . ., including their superpositions: A|2Ni+B|2N+1i. Whereas the circular superpositions of squeezed coherent states allow to get a more large family of Fock states, namely,¯¯k2N®, k = 1, 2, 3, .... An alternative proposal to measure the Wigner function and a device to implement the condicional displacement operation for traveling fields are presented - appropriate to create new superpositions, like, |Ãi± ˆD(®)|Ãi, which includes interesting particular cases.
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    ABSTRACT: In this thesis we investigate the dynamics of cold atoms in optical cavities. We study how the scattering properties of laser driven atoms are modified by the presence of an optical resonator. This investigation can be divided into two parts. First, we study the scaling of the scattering properties with the number of atoms, and we show in particular how Bragg scattering by an atomic lattice is modified by the presence of the resonator. In this case, the atoms are trapped at the antinodes of the cavity mode function by the mechanical potential induced by the resonator. In a second part, we show how this modification of the scattering properties can be used for efficiently cooling single atoms to the ground state of a harmonic trap. In particular, we find that the motion is critically affected by quantum correlations induced by the mechanical coupling with the resonator, which may lead to selective suppression of certain transitions for the appropriate parameters regimes, thereby increasing the cooling efficiency.
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