Bulletin of the American Physical Society
2008 APS March Meeting
Volume 53, Number 2
Monday–Friday, March 10–14, 2008; New Orleans, Louisiana
Session W14: Quantum Optics |
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Sponsoring Units: DAMOP Chair: Mark Edwards, Georgia Southern University Room: Morial Convention Center 205 |
Thursday, March 13, 2008 2:30PM - 2:42PM |
W14.00001: Quantum analysis of nonlinear beam splitter with second order nonlinearity. Hari Prakash, Devendra Kumar Mishra A linear beam splitter mixes two input modes having annihilation operators $\hat {a}$ and $\hat {b}$ and generate two output modes having annihilation operators $\hat {c}$and $\hat {d}$, which are linear in $\hat {a}$ and $\hat {b}$and may be written as $\hat {c}=t\hat {a}+ir\hat {b}$ and $\hat {d}=t\hat {b}+ir\hat {a}$, where t and r are the real coefficients of transmission and reflection, respectively, with r$^{2}$ + t$^{2}$ =1. We include the second order nonlinearity and as a result we find generation of second- harmonic non-classical light. If two coherent beams are mixed at input, squeezing and sub-Poissonian photon statistics are seen to be exhibited by the second-harmonic output beam. [Preview Abstract] |
Thursday, March 13, 2008 2:42PM - 2:54PM |
W14.00002: Quantum control of EIT dispersion via atomic tunneling in a double-well Bose-Einstein condensate James Weatherall, Christopher Search, Markku Jaaskelainen We consider electromagnetically induced transparency (EIT) in an atomic Bose-Einstein Condensate (BEC) trapped in a double well potential. A weak probe propagates through one of the wells and interacts with atoms in a three-level $\Lambda$ configuration. The well through which the probe propagates is dressed by a strong control beam with Rabi frequency $\Omega_{\mu}$, as in standard EIT systems. Tunneling between the wells at the frequency $g$ provides a coherent coupling between identical electronic states in the two wells that leads to the formation of inter-well dressed states. The tunnel coupling results in the formation of two ultra-narrow absorption resonances for the probe field that are inside of the ordinary EIT transparency window, which can be interpreted in terms of the inter-well dressed states and the formation of a novel type of dark state involving the coupling laser and the inter-well tunneling. To either side of these ultra-narrow resonances there is normal dispersion with ultra-large slope controlled by $g$. For realistic values of $g$, the large slope of this dispersion yields group velocities for the probe field that are two orders of magnitude slower than standard EIT systems. Additionally, we discuss the effects of the inter-well coupling on the nonlinear susceptibility, $\chi^{(3)}$. [Preview Abstract] |
Thursday, March 13, 2008 2:54PM - 3:06PM |
W14.00003: Electromagnetically-induced transparency (EIT) in a four-level atom system Chris Nelson, Cristian Bahrim We prove that the EIT technique can be used for slowing down \textit{simultaneously} two circularly--left and --right polarized laser pulses (probe fields) in the presence of a linearly polarized laser pulse (coupling field) using a four-level atom system prepared with a weak B-field. The simultaneous quantum interference between the coupling field and each of the two probe fields leads to the formation of a new type of EIT system: a \textbf{W-system}. By turning off one of the two probe fields, a standard EIT behavior can be recognized in two independent V-systems. Our novel EIT technique is applied to ultra-cold Mg atoms in low-lying states ($^{1}$S$_{0 }$-- ground state and $^{1}$P$_{1}$ -- first excited state). The density matrix formalism is employed for finding coherences between Zeeman levels of the upper $^{1}$P$_{1}$ state in our W-system. Solving the master equation for a population-trapped four-level atom system and assuming a zero population density on the Zeeman levels of the $^{1}$P$_{1}$ state give atomic susceptibilities for the dark states associated to the two probe fields. The analysis of the EIT behavior in our W-system is done by varying (1) the Rabi frequencies for the triplet $^{1}$P$_{1 }$state and (2) the detuning of the two probe lasers. The dependence of the EIT features with the B-field is also discussed. [Preview Abstract] |
Thursday, March 13, 2008 3:06PM - 3:18PM |
W14.00004: Coherent optical spectroscopy of a strongly coupled semiconductor microcavity quantum-dot system Kartik Srinivasan, Oskar Painter Chip-based systems involving a semiconductor microcavity coupled to an embedded quantum dot (QD) offer a scalable, stable platform for optical cavity quantum electrodynamics. To harness this potential in a manner consistent with many protocols for quantum information processing, the system must be coherently probed and manipulated. However, experiments in these systems have largely relied on incoherent excitation through photoluminescence (PL). Here, we describe recent experiments [1] in which a fiber taper waveguide is used to perform steady-state coherent linear and nonlinear optical spectroscopy of a strongly coupled microcavity-QD system, probing the system on its photonic channel (rather than its matter channel, as in PL). Under weak driving, vacuum Rabi splitting is observed, while increasing the drive strength reveals saturation for an average intracavity photon number of less than one. [1] K. Srinivasan and O. Painter (2007), to appear in Nature, Dec. 6, 2007 (preprint: physics/0707.3311). [Preview Abstract] |
Thursday, March 13, 2008 3:18PM - 3:30PM |
W14.00005: Monitoring electron spin decoherence in a quantum dot by weak measurement Shu Hong Fung, Renbao Liu Based on the fluctuation-dissipation theorem, information about the dynamics of a system could be derived by noise spectra with passive probe, in lieu of active pump-control-probe procedures. For a quantum system, the passive probe still needs to be weak lest the system is disturbed by state collapse. We consider the weak measurement by Faraday rotation (FR) of a single spin in a quantum dot under an external magnetic field in the Voigt configuration. The quantum dot is repeatedly probed by linearly polarized laser pulses. The FR caused by a single spin is extremely small (about a few millionth rad), so the photon states with different rotation angles, and hence the electrons spin states, are only weakly distinguished. The polarized light beam is filtered by a polarized beam splitter and the reflected photons are counted. The second order correlation of the photon count shot noise oscillates with a rapid damping caused by the inhomogeneous broadening (which exists even for a single spin under repeated measurements). In the third order correlation, the single spin decoherence is singled out from the rapid inhomogeneous dephasing, which would otherwise require spin echo. [Preview Abstract] |
Thursday, March 13, 2008 3:30PM - 3:42PM |
W14.00006: Spontaneous emission from a tunneling atom Daniel Braun, John Martin We study the tunneling of a two-level atom in a double well potential in while the atom couples either to a single electromagnetic field mode of a cavity to the full continuum of electromagnetic modes in three dimensions. Both studies are within the Lamb-Dicke regime concerning transitions to higher vibrational states, but beyond the Lamb-Dicke regime concerning the tunneling split groundstate. The first case leads to an extended Jaynes-Cummings model which can be solved exactly. We show that the coupling between internal and external degrees of freedom of the atom induced by the cavity mode can dramatically change the tunneling behavior. In general the tunneling process becomes quasiperiodic. If the cavity is fed with a coherent state, a collapse and revival of the tunneling can occur. Accessing the internal degrees of freedom of the atom with a laser allows to coherently manipulate the atom position, and in particular to prepare the atom in one of the two wells. In the second case, the tunneling process may decohere, depending on the wavelength corresponding to the internal transition and on the spontaneous emission rate. Interference fringes appear in the emitted light from a tunneling atom, or an atom in a stationary coherent superposition of its center--of--mass motion, if the wavelength is comparable to the well separation and if the external state of the atom is post-selected.\newline [1] J.~Martin and D.~Braun, arXiv:0704.0763 and arXiv:0707.4158. [Preview Abstract] |
Thursday, March 13, 2008 3:42PM - 3:54PM |
W14.00007: Single photon nonlinearities using arrays of cold polar molecules T. Bragdon, R. M. Rajapakse, A. M. Rey, S. F. Yelin We model single photon nonlinearity via dipole-dipole interaction in cold polar molecules using the protected Dicke-like symmetric manifold for potential optical quantum computation processing. We report on potential decoherences described by phonon dispersion, spontaneous, and stimulated decays. We compare to individually addressed molecules from previous work, and discuss briefly the feasibility in optical quantum computation processing as an element of a controlled-Z gate. [Preview Abstract] |
Thursday, March 13, 2008 3:54PM - 4:06PM |
W14.00008: Fermionization of strongly interacting photons in one-dimensional nonlinear medium Darrick Chang, Vladimir Gritsev, Giovanna Morigi, Vladan Vuletic, Mikhail Lukin, Eugene Demler Understanding strongly correlated quantum systems is a central problem in many areas of physics. The collective behavior of interacting particles gives rise to diverse fundamental phenomena such as confinement in quantum chromodyanmics, spontaneous symmetry breaking and phase transitions, and electron fractionalization in one dimensional systems and in the quantum Hall regime. While such systems typically involve strongly interacting massive particles, optical photons can also interact with each other in a nonlinear medium. In practice, however, such interactions are typically very weak. We describe a novel technique that allows the creation of a strongly correlated quantum gas of photons, which is made possible by the tight field confinement that can be achieved in a number of novel, one-dimensional optical systems. This confinement enables the generation of large optical nonlinearities via the interaction of photons with a nearby cold atomic gas, which can be further amplified by an optical Bragg grating that traps these photons within the medium. In its extreme, we show that a quantum light field can undergo {\it fermionization} in such one-dimensional media, which can be probed via standard photon correlation measurements. Realization of such systems can open a route for quantum simulators of {\it matter} Hamiltonians using light fields and novel applications in metrology and quantum information. [Preview Abstract] |
Thursday, March 13, 2008 4:06PM - 4:18PM |
W14.00009: Entangled-photon absorption in semiconductor nanostructures Felipe Vallejo, Luis Quiroga We present a comparative study of two-photon absorption by semiconductor nanostructures for two kind of light: (i) Light with wave-like classical properties (laser light) and (ii) A new type of quantum entangled light. First, we report on results concerning entangled-photon absorption processes due to $s$ and $d$ final states in core-shell quantum dots. Second, within the framework of the effective-mass approximation both the classical as well as the entangled two-photon absorption in quantum wells (QWs) and quantum wires (QWRs) have been addressed. Results for non-entangled light with polarization both parallel and perpendicular to the directions of confinement are in perfect agreement with the ones already known. We proceed to extend those results to the less explored case of entangled light absorption in semiconductor nanostructures. The absorption spectra for entangled light is richer in structure and complexity as compared with the classical light case. We find that the absorption rate (cross-section) for entangled light depends additionally of a new important parameter, the entanglement time $T_e$, which gives rise to quantum interference effects. As a result, entangled photons produce entangled-induced transparencies. [Preview Abstract] |
Thursday, March 13, 2008 4:18PM - 4:30PM |
W14.00010: Photon Tunneling Through Dielectric Bandgaps and Evanescent Gaps Natalia Rutter, Sergey Polyakov, Paul Lett, Alan Migdall We implement an optical tunneling testbed using the precise simultaneity of creation of twin photons produced by parametric down conversion and a Hong-Ou-Mandel interferometer. With this setup, we can measure photon traversal times of a sample with fs precision. We use this setup to compare the time for a photon to traverse dielectric stacks of odd versus even numbers of layers of alternating indexes of refraction. Preliminary data shows that subtle changes in the stack structure result in dramatic variations in photon traversal times ($\sim $10 fs) that can range from sub- to super-luminal. Our ultimate goal is to use this setup to investigate photon tunneling times in regions of true evanescent propagation and compare them to the traversal times in our dielectric stack bandgap samples where the propagation is oscillatory. This allows us to test the suitability of certain optical models of tunneling and highlight the pitfalls that occur when relying on conditional measurements. [Preview Abstract] |
Thursday, March 13, 2008 4:30PM - 4:42PM |
W14.00011: Nonlinear wave scattering by small barrier potentials Wenjie Wan, Jason W. Fleischer Scattering by a barrier potential is a fundamental problem in wave physics, involving issues of boundary conditions, resonances, radiation, etc. While scattering in the linear case is well-known, the nonlinear case has received far less attention. In the nonlinear regime, self-interaction affects tunneling and re-radiation dynamics, often leading to new topological structures (e.g. dark solitons and vortices). Examples include many-body quantum systems, plasmas, and nonlinear optics. Here, we focus on the optical case by considering plane-wave scattering from an optically-induced barrier potential (step index) inside a photorefractive crystal. We experimentally demonstrate shock wave formation (dark soliton trains) in 1D and vortex generation in 2D, as a function of barrier height and input wave angle. We show numerically that these results arise from a combination of tunneling, scattering, and optical superflow around the boundary. Applications both within and beyond optics will be discussed. [Preview Abstract] |
Thursday, March 13, 2008 4:42PM - 4:54PM |
W14.00012: Photon localization and Dicke superradiance in atomic gases: crossover to a ``small world'' network Eric Akkermans, Aharon Gero, Robin Kaiser We study photon propagation in a gas of $N$ atoms, using an effective Hamiltonian that accounts for photon mediated atomic dipolar interactions. The configuration average density $P(\Gamma)$ of photon escape rates is obtained from the spectrum of the $N \times N$ random matrix $\Gamma_{ij} = \sin (x_{ij}) / x_{ij}$, where $x_{ij}$ is the dimensionless random distance between any two atoms expressed in units of the photon wavelength. A scaling function is defined to study photons escape rates as a function of disorder and system size. We show that for a strong enough disorder, photons do not escape the gas. This localization is described using a mapping of this problem onto statistical properties of random networks. We show that there is no localization phase transition as expected in disordered systems without correlation, but rather a cross-over between localized and delocalized photons. The mean field solution of this problem displays a ``small world'' behavior. In the Dicke limit, we recover localization associated to cooperative effects. [Preview Abstract] |
Thursday, March 13, 2008 4:54PM - 5:06PM |
W14.00013: Fermi two atom problem in extended Fredrichs-Lee Model Kavan Modi, James Zabel, George Sudarshan In 1932 Fermi calculated the time required for excitation transition between two atoms. He found the minimum time to be the distance between the atoms divided by the speed of light. Recently, Hegerfeldt, using a very basic argument of analyticity of the wavefunction, showed that the excitation amplitude of the second atom must be finite for all times or zero for all times. We are studying this problem in detail using a modified Fredrichs-Lee model where two discrete states are connected by a continuum. We can solve for the transition amplitude exactly in our model, without assuming that a photon is the mediator between the two discrete modes. Our model should shed some light on the conceptual difficulties that have bothered the community for long. [Preview Abstract] |
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