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M. Suhail Zubairy

Publications and source records attributed to M. Suhail Zubairy.

68 records · Page 4Linked to original sources
arXiv2007

Planck, Photon Statistics, and Bose-Einstein Condensation

The interplay between optical and statistical physics is a rich and exciting field of study. Black body radiation was the first application of photon statistics, although it was initially treated as a problem of the cavity oscillators in equilibrium with the photon field. However Planck surprisingly resisted the idea that anything physical would be quantized for a long time after he had solved the problem. We trace this development. Then, after the invention of the laser itself, it proved difficult to develop a theory of laser action that could account for photon statistics, i.e. fluctuations near threshold. This was accomplished in 1965. After Bose-Einstein condensation was successfully achieved, the same problem arose in this case. The fluctuation problem had not been treated adequately even for the ideal Bose gas. However this problem has now been solved using the same techniques as in the theory of laser action.

physics.optics↗
arXiv2007

Control of Goos-Hanchen shift of a light beam via a coherent driving field

We present a proposal to manipulate the Goos-Hanchen shift of a light beam via a coherent control field, which is injected into a cavity configuration containing the two-level atomic medium. It is found that the lateral shifts of the reflected and transmitted probe beams can be easily controlled by adjusting the intensity and detuning of the control field. Using this scheme, the lateral shift at the fixed incident angle can be enhanced (positive or negative) under the suitable conditions on the control field, without changing the structure of the cavity.

physics.optics↗
arXiv2006

Entanglement conditions for two-mode states: Applications

We examine the implications of several recently derived conditions [Hillery and Zubairy, Phys. Rev. Lett. 96, 050503 (2006)] for determining when a two-mode state is entangled. We first find examples of non-Gaussian states that satisfy these conditions. We then apply the entanglement conditions to the study of several linear devices, the beam splitter, the parametric amplifier, and the linear phase-insensitive amplifier. For the first two, we find conditions on the input states that guarantee that the output states are entangled. For the linear amplifier, we determine in the limit of high and no gain, when an entangled input leads to an entangled output. Finally, we show how application of two two-mode entanglement conditions to a three-mode state can serve as a test of genuine three-mode entanglement.

quant-ph↗
arXiv2006

Entanglement conditions for two-mode states

We provide a class of inequalities whose violation shows the presence of entanglement in two-mode systems. We initially consider observables that are quadratic in the mode creation and annihilation operators and find conditions under which a two-mode state is entangled. Further examination allows us to formulate additional conditions for detecting entanglement. We conclude by showing how the methods used here can be extended to find entanglement in systems of more than two modes.

quant-ph↗
arXiv2006

Single-atom as a macroscopic entanglement source

We discuss the generation of a macroscopic entangled state in a single atom cavity-QED system. The three-level atom in a cascade configuration interacts dispersively with two classical coherent fields inside a doubly resonant cavity. We show that a macroscopic entangled state between these two cavity modes can be generated under large detuning conditions. The entanglement persists even under the presence of cavity losses.

quant-ph↗
arXiv2006

Spectral Narrowing via Quantum Coherence

We have studied the transmission of an optically thick Rb vapor that is illuminated by monochromatic and noise broaden laser fields in Lambda configuration. The spectral width of the beat signal between the two fields after transmission through the atomic medium is more than 1000 times narrower than the spectral width of this signal before the medium.

quant-ph↗
arXiv2006

Measurement of the separation between atoms beyond diffraction limit

Precision measurement of small separations between two atoms or molecules has been of interest since the early days of science. Here, we discuss a scheme which yields spatial information on a system of two identical atoms placed in a standing wave laser field. The information is extracted from the collective resonance fluorescence spectrum, relying entirely on far-field imaging techniques. Both the interatomic separation and the positions of the two particles can be measured with fractional-wavelength precision over a wide range of distances from bout lambda/550 to lambda/2.

quant-ph↗
arXiv2005

Subwavelength atom localization via amplitude and phase control of the absorption spectrum-II

Interaction of the internal states of an atom with spatially dependent standing-wave cavity field can impart position information of the atom passing through it leading to subwavelength atom localization. We recently demonstrated a new regime of atom localization [Sahrai {\it et al.}, Phys. Rev. A {\bf 72}, 013820 (2005)], namely sub-half-wavelength localization through phase control of electromagnetically induced transparency. This regime corresponds to extreme localization of atoms within a chosen half-wavelength region of the standing-wave cavity field. Here we present further investigation of the simplified model considered earlier and show interesting features of the proposal. We show how the model can be used to simulate variety of energy level schemes. Furthermore, the dressed-state analysis is employed to explain the emergence and suppression of the localization peaks, and the peak positions and widths. The range of parameters for obtaining clean sub-half-wavelength localization is identified.

quant-ph↗
arXiv2005

Subwavelength atom localization via amplitude and phase control of the absorption spectrum

We propose a scheme for subwavelength localization of an atom conditioned upon the absorption of a weak probe field at a particular frequency. Manipulating atom-field interaction on a certain transition by applying drive fields on nearby coupled transitions leads to interesting effects in the absorption spectrum of the weak probe field. We exploit this fact and employ a four-level system with three driving fields and a weak probe field, where one of the drive fields is a standing-wave field of a cavity. We show that the position of an atom along this standing wave is determined when probe field absorption is measured. We find that absorption of the weak probe field at a certain frequency leads to subwavelength localization of the atom in either of the two half-wavelength regions of the cavity field by appropriate choice of the system parameters. We term this result as sub-half-wavelength localization to contrast it with the usual atom localization result of four peaks spread over one wavelength of the standing wave. We observe two localization peaks in either of the two half-wavelength regions along the cavity axis.

quant-ph↗
arXiv2005

Phase control of electromagnetically induced transparency and its applications to tunable group velocity and atom localization

We show that, by simple modifications of the usual three-level $Λ$-type scheme used for obtaining electromagnetically induced transparency (EIT), phase dependence in the response of the atomic medium to a weak probe field can be introduced. This gives rise to phase dependent susceptibility. By properly controlling phase and amplitudes of the drive fields we obtain variety of interesting effects. On one hand we obtain phase control of the group velocity of a probe field passing through medium to the extent that continuous tuning of the group velocity from subluminal to superluminal and back is possible. While on the other hand, by choosing one of the drive fields to be a standing wave field inside a cavity, we obtain sub-wavelength localization of moving atoms passing through the cavity field.

quant-ph↗
arXiv2004

Quantum electrodynamics of accelerated atoms in free space and in confined cavities

We consider a gedanken experiment with a beam of atoms in their ground state that are accelerated through a single-mode microwave cavity. We show that taking into account of the ''counter-rotating'' terms in the interaction Hamiltonian leads to the excitation of an atom with simultaneous emission of a photon into a field mode. In the case of a slow switching on of the interaction, the ratio of emission and absorption probabilities is exponentially small and is described by the Unruh factor. In the opposite case of sharp cavity boundaries the above ratio is much greater and radiation is produced with an intensity which can exceed the intensity of Unruh acceleration radiation in free space by many orders of magnitude. In both cases real photons are produced, contrary to the opinion that a uniformly accelerated atom does not radiate. The cavity field at steady state is described by a thermal density matrix. However, under some conditions laser gain is possible. We present a detailed discussion of how the acceleration of atoms affects the generated cavity field in different situations, progressing from a simple physical picture of Unruh radiation to more complicated situations.

quant-ph↗
arXiv2003

Propagation of Fronts and Information in Dispersive Media

We present a general proof based on Kramers-Kronig relations that, in a normal or anomalous dispersive linear medium, any (discontinuitynonanalytic disturbance) in an electromagnetic pulse can not propagate faster than the phase velocity, $c$. Consequently the information carried by the discontinuity (nonanalytical disturbance) can not be transmitted superluminally.

physics.class-ph↗