@article{HenkelGardinerNegretti2004,
author = {Henkel, Carsten and Gardiner, Simon A. and Negretti, Antonio},
title = {(De)coherence physics with condensates in microtraps},
issn = {1054-660X},
year = {2004},
abstract = {We discuss the dynamics of a condensate in a miniaturized electromagnetic trap formed above a microstructured substrate. Recent experiments have found that trap lifetimes get reduced when approaching the substrate because atoms couple to thermally excited near fields. The data agree quantitatively with our theory [Appl. Phys. B 69, 379 (1999)]. We focus on the decoherence of a quantum degenerate gas in a quasi-one-dimensional trap. Monte Carlo simulations indicate that atom interactions reduce the condensate decoherence rate. This is explained by a simple theory in terms of the suppression of long-wavelength excitations. We present preliminary simulation results for the adiabatic generation of dark solitons},
language = {en}
}
@article{CironeNegrettiCalarcoetal.2005,
author = {Cirone, M. A. and Negretti, Antonio and Calarco, T. and Kr{\"u}ger, P. and Schmiedmayer, J{\"o}rg},
title = {A simple quantum gate with atom chips},
year = {2005},
abstract = {We present a simple scheme for implementing an atomic phase gate using two degrees of freedom for each atom and discuss its realization with cold rubidium atoms on atom chips. We investigate the performance of this collisional phase gate and show that gate operations with high fidelity can be realized in magnetic traps that are currently available on atom chips},
language = {en}
}
@article{CockburnNegrettiProukakisetal.2011,
author = {Cockburn, S. P. and Negretti, Antonio and Proukakis, N. P. and Henkel, Carsten},
title = {Comparison between microscopic methods for finite-temperature Bose gases},
series = {Physical review : A, Atomic, molecular, and optical physics},
volume = {83},
journal = {Physical review : A, Atomic, molecular, and optical physics},
number = {4},
publisher = {American Physical Society},
address = {College Park},
issn = {1050-2947 (print)},
doi = {10.1103/PhysRevA.83.043619},
pages = {29},
year = {2011},
abstract = {We analyze the equilibrium properties of a weakly interacting, trapped quasi-one-dimensional Bose gas at finite temperatures and compare different theoretical approaches. We focus in particular on two stochastic theories: a number-conserving Bogoliubov (NCB) approach and a stochastic Gross-Pitaevskii equation (SGPE) that have been extensively used in numerical simulations. Equilibrium properties like density profiles, correlation functions, and the condensate statistics are compared to predictions based upon a number of alternative theories. We find that due to thermal phase fluctuations, and the corresponding condensate depletion, the NCB approach loses its validity at relatively low temperatures. This can be attributed to the change in the Bogoliubov spectrum, as the condensate gets thermally depleted, and to large fluctuations beyond perturbation theory. Although the two stochastic theories are built on different thermodynamic ensembles (NCB, canonical; SGPE, grand-canonical), they yield the correct condensate statistics in a large Bose-Einstein condensate (BEC) (strong enough particle interactions). For smaller systems, the SGPE results are prone to anomalously large number fluctuations, well known for the grand-canonical, ideal Bose gas. Based on the comparison of the above theories to the modified Popov approach, we propose a simple procedure for approximately extracting the Penrose-Onsager condensate from first-and second-order correlation functions that is both computationally convenient and of potential use to experimentalists. This also clarifies the link between condensate and quasicondensate in the Popov theory of low-dimensional systems.},
language = {en}
}
@article{NegrettiHenkel2004,
author = {Negretti, Antonio and Henkel, Carsten},
title = {Enhanced phase sensitivity and soliton formation in an integrated BEC interferometer},
issn = {0953-4075},
year = {2004},
abstract = {We study the dynamics of Bose-Einstein condensates in time-dependent microtraps for the purpose of understanding the influence of the mean field interaction on the performance of interferometers. We identify conditions where the nonlinearity due to atom interactions increases the sensitivity of interferometers to a phase shift. This feature is connected with the adiabatic generation of a dark soliton. We analyse the robustness of this phenomenon with respect to thermal fluctuations, due to excited near fields in an electromagnetic surface trap},
language = {en}
}
@article{NegrettiCalarcoCironeetal.2005,
author = {Negretti, Antonio and Calarco, T. and Cirone, M. A. and Recati, A.},
title = {Performance of quantum phase gates with cold trapped atoms},
year = {2005},
abstract = {We examine the performance of a quantum phase gate implemented with cold neutral atoms in microtraps, when anharmonic traps are employed and the effects of finite temperature are also taken into account. Both the anharmonicity and the temperature are found to pose limitations to the performance of the quantum gate. We present a quantitative analysis of the problem and show that the phase gate has a high quality performance for the experimental values that are presently or in the near future achievable in the laboratory},
language = {en}
}
@article{CharronCironeNegrettietal.2006,
author = {Charron, Eric and Cirone, M. A. and Negretti, Antonio and Schmiedmayer, J{\"o}rg and Calarco, Tommaso},
title = {Theoretical analysis of a realistic atom-chip quantum gate},
issn = {1050-2947},
year = {2006},
abstract = {We present a detailed, realistic analysis of the implementation of a proposal for a quantum phase gate based on atomic vibrational states, specializing it to neutral rubidium atoms on atom chips. We show how to create a double-well potential with static currents on the atom chips, using for all relevant parameters values that are achieved with present technology. The potential barrier between the two wells can be modified by varying the currents in order to realize a quantum phase gate for qubit states encoded in the atomic external degree of freedom. The gate performance is analyzed through numerical simulations; the operation time is similar to 10 ms with a performance fidelity above 99.9\%. For storage of the state between the operations the qubit state can be transferred efficiently via Raman transitions to two hyperfine states, where its decoherence is strongly inhibited. In addition we discuss the limits imposed by the proximity of the surface to the gate fidelity.},
language = {en}
}