Bulletin of the American Physical Society
38th Annual Meeting of the Division of Atomic, Molecular, and Optical Physics
Volume 52, Number 7
Tuesday–Saturday, June 5–9, 2007; Calgary, Alberta, Canada
Session J5: Cavity QED and Quantum Control |
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Chair: P. Xue, University of Calgary Room: TELUS Convention Centre Glen 205 |
Thursday, June 7, 2007 1:30PM - 1:42PM |
J5.00001: Blue trapping and dispersive observation of single atoms. T. Puppe, I. Schuster, A. Grothe, A. Kubanek, K. Murr, P.W.H. Pinkse, G. Rempe A single atom strongly coupled to a high-finesse cavity constitutes a fundamental quantum system of matter-light interaction. An established tool to localize an atom in the cavity mode is the optical dipole trap. So far, only red-detuned dipole traps have been demonstrated in cavity QED. Since the atom is trapped in a region of high intensity, the AC-Stark effect shifts the atomic energy levels. We store single atoms in a blue-detuned intracavity dipole trap. Here, the Stark shift vanishes while the atom is strongly coupled to a cavity mode. Strong coupling and a Stark shift much smaller than the trap height is directly observed in the normal-mode spectroscopy. The blue trap allows us to explore the regime of dispersive atom-light interaction. As a practical application, we demonstrate that a single atom, can efficiently be detected while spontaneously scattering only a few photons. The realization of the blue intracavity dipole trap now allows measurements in cavity QED while preserving the free-space properties of the atom. [Preview Abstract] |
Thursday, June 7, 2007 1:42PM - 1:54PM |
J5.00002: Deterministic Loading of Single Atoms in an Optical Cavity Soo Kim, Kevin Fortier, Michael Gibbons, Michael Chapman To utilize a single atom as a qubit in cavity QED requires exquisite control over both the internal and external degrees of freedom of the atom. In our experiment, a single rubidium atom is captured in a high gradient MOT. The atom is loaded into a 1-D optical lattice and then transported 8 mm to a high finesse optical cavity. The atoms are stored and continuously observed in the cavity for up 10 s by employing a cavity-assisted cooling scheme. With submicron control of position of the atom, we have studied the spatial dependence of the atom-cavity coupling. We present our recent results and future prospects. [Preview Abstract] |
Thursday, June 7, 2007 1:54PM - 2:06PM |
J5.00003: An atom chip for studying interactions between atoms and metal surfaces J.D. Carter, O. Cherry, J.D.D. Martin Magnetic microtraps (atom chips) typically use $\mu$m scale current-carrying wires on a substrate to confine cold atoms in magnetic field minima. The high field gradients achievable in such devices can be used to create small clouds of atoms at well-defined (and variable) distances from the surface of a chip. \textit{In situ} excitation of the trapped atoms to Rydberg states can be conveniently used to investigate interactions between Rydberg atoms and the surface of the chip, without the complication of atomic motion inherent in experiments using atomic beams. However, stray electric fields from the current-carrying wires make Rydberg excitation problematic. To overcome this problem, we have fabricated a chip with an electrostatic shield over the wires. We will present preliminary experimental results using \textsuperscript{87}Rb and discuss the effects of inhomogeneous electric fields due to surface imperfections. [Preview Abstract] |
Thursday, June 7, 2007 2:06PM - 2:18PM |
J5.00004: ABSTRACT WITHDRAWN |
Thursday, June 7, 2007 2:18PM - 2:30PM |
J5.00005: Nonlinear Optics of Ultracold Atoms in an Optical Cavity. Kater Murch, Kevin Moore, Subhadeep Gupta, Dan Stamper-Kurn We report observations of non-linear optical phenomena in an ultracold atomic gas in a Fabry-Perot cavity in the single atom strong coupling regime. Up to 5 x 10$^{4} \quad ^{87}$Rb atoms are trapped at the antinodes of an in-cavity far-off resonance optical standing wave. We have observed significant Kerr non-linearity and dispersive optical bistability in the transmission of a probe beam through the cavity at our lowest detectable intensities corresponding to 10$^{-2}$ photons in the cavity. The non-linear index of refraction responsible for these effects arises from the collective motion of atoms in the combined potential of the trap and probe. [Preview Abstract] |
Thursday, June 7, 2007 2:30PM - 2:42PM |
J5.00006: Dipole potential in a cavity: Bistable or not? Dominic Meiser The motion of an atom in a far red detuned light field inside a resonantly driven cavity has surprising and counter intuitive features because atoms and cavity field comprise an open quantum system exchanging energy and momentum with the environment. A dilemma arising in this context is whether the atom is attracted to the antinodes of the field where the derivative of the intensity with respect to atomic position vanishes or to some point away from the anti-node where it tunes the cavity less out of resonance such that the intensity at its location is maximum. We study this problem using a microscopic model that avoids the ad-hoc introduction of semiclassical force concepts. If the trapping is provided by few photons in the strong coupling regime, we find that the atom's wavefunction collapses near resonant points away from the field antinodes due to measurements on the cavity field. In the limit of large photon numbers a generally non-conservative semiclassical force with an equilibrium point at the field antinode emerges. [Preview Abstract] |
Thursday, June 7, 2007 2:42PM - 2:54PM |
J5.00007: Coherent anti-Stokes Raman scattering microscopy in a microcavity Michele Marrocco The combination of nonlinear spectroscopy and cavity QED is a stimulating field of research [see, for example, S. M. Spillane et al., Nature 415, 621 (2002)]. In this work, coherent anti-Stokes Raman scattering (CARS) taking place within a microcavity with parallel mirrors, is studied. The interest stems from the fact that CARS is a powerful nonlinear spectroscopic technique, particularly useful in imaging of microscopic samples [A. Zumbusch et al., Phys. Rev. Lett. 82, 4142 (1999)]. The theory of CARS microscopy applied to a sample placed within the microcavity is developed and the calculated CARS power in comparison with its free-space value shows the characteristic oscillation between inhibition and enhancement. If d and lambda indicate the cavity spacing and the anti-Stokes wavelength, inhibition is then found for d smaller than lambda and becomes complete only for microscope objectives operated in dry conditions. It is also found that the first enhancement at d=lambda is more relevant for microscopes with smaller numerical apertures. Higher numerical apertures, instead, reveal weaker cavity effects as a consequence of the larger collection efficiency. [Preview Abstract] |
Thursday, June 7, 2007 2:54PM - 3:06PM |
J5.00008: Coherent Control of Molecular Ion Production in Cold Rb Vapor M.L. Trachy, G. Veshapidze, M.H. Shah, H.U. Jang, B.D. DePaola When Rb vapor is exposed to pulses of light from an ultra-fast laser having a central wavelength of about 800~nm, the result is a very large number of atomic Rb ions. This is because, within the bandwidth of the laser pulse, resonant three-photon ionization takes place along the ladder Rb(5s) $\rightarrow$ Rb (5p) $\rightarrow$ Rb(5d) $\rightarrow$~$\epsilon l$. The first transition is at 780~nm, the second is at 776~nm, and the third is anything shorter than 1252~nm. Virtually no molecular ions are formed in the interaction of the optical pulse with the Rb vapor. In a series of experiments we show that this natural trend can be reversed, with greatly reduced Rb$^+$ production and greatly increased Rb$_2^+$ production. Partly this is accomplished by introducing a weak, quasi-cw diode laser, nearly resonant with the Rb(5p) $\rightarrow$ Rb(4d) transition. However, an important component in switching from Rb$^+$ to Rb$_2^+$ production is shaping the ultra-fast pulse in the frequency and phase domains, putting ``notches" in the beam at crucial wavelengths and adjusting the ``chirp" of the pulse. For example, removing wavelengths near the D1 and Rb (5p) $\rightarrow$ Rb(5d) transitions reduced Rb$^+$ production by nearly two orders of magnitude. A detailed discussion of these and related results will be given. [Preview Abstract] |
Thursday, June 7, 2007 3:06PM - 3:18PM |
J5.00009: Circuit QED transducers for quantum electromechanical systems Gerard Milburn, Hsi-Sheng Goan, Louise Kettle, Matthew Wooley We consider a very high frequency nano-mechanical oscillator coupled to a superconducting co planar microwave resonator. The microwave cavity is modeled as a single mode cavity coupled to the nano-mechanical oscillator displacement. In this configuration the microwave cavity acts as a transducer for the motion of the nano-mechanical oscillator. If the coupling is strong the system may exhibit sub/second harmonic generation in analogy to optical second order nonlinear behavior. We also show how the bifurcation of the steady state to limit cycle dynamics in this system could be used as a bifurcation amplifier for readout of a single solid state qubit. We calculate the noise on the limit cycle and assess how well it can function as a single qubit readout device. We also consider the case of weak coupling with parametric driving of the nano-mechanical resonator. In this case mechanical squeezing occurs and may be detected in the microwave field. We calculate the observed noise power spectrum for the microwave field with realistic experimental parameters. [Preview Abstract] |
Thursday, June 7, 2007 3:18PM - 3:30PM |
J5.00010: Synthesis of Arbitrary States of Large Atomic Spins by Quantum Control Souma Chaudhury, Seth Merkel, Tobias Herr, Ivan Deutsch, Poul Jessen A spin 1/2 system is fully controllable by applying geometric rotations with magnetic fields, however for larger spins typical for alkali atom ground states, one needs additional unitary transformations to achieve controllability. We demonstrate universal quantum control of the spin-angular momentum associated with the lower hyperfine ground state of individual 133Cs atoms (F=3), by driving the system with magnetic fields and a rank-2 tensor light shift induced by a near-resonant laser field. A relatively simple optimization routine can be used to design time dependent controls that transform an initial fiducial state $|F=3,mf=3\rangle$ into a desired target state. In a series of experiments we have used this procedure to generate a broad range of target states, including squeezed and other non-classical states. In general we achieve yields (fidelity of the actual state relative to the target state) in the range $\sim 85\% - 90\%$, limited mostly by errors in the control fields and by light scattering. We compare this approach to an adiabatic method of synthesizing spin-squeezed states and discuss its applications relating to quantum information and metrology. [Preview Abstract] |
Thursday, June 7, 2007 3:30PM - 3:42PM |
J5.00011: Long-range interactions and many-body effects in a cold Rydberg gas Robin C\^ot\'e, Jovica Stanojevic In recent years, the unique combination of properties of ultracold Rydberg atoms, such as long radiative lifetimes or strong long-range interactions, has led to proposals for using them to implement fast quantum gates. Here, we explore the behavior of macroscopic atomic samples where laser excitation of ultracold atoms to high-lying Rydberg states is locally blockaded due to the strong van der Waals interactions between Rydberg atoms. We discuss a mean-field model that defines local blockade domains and agrees well with experimental observations. In a $N$-atom mesoscopic sample under perfect blockade condition, the single excitation is described by a many-body Rabi frequency, {\it i.e.} $\sin^2 (\sqrt{N}\Omega \tau )$. Here, we generalize the result to a macroscopic sample with several ``domains" containing effectively $N_{\rm eff}$ atoms; the number of excited atoms is then $ N_{\rm exc} \sim \sum_{\rm domain}\sin^2 \left(\sqrt{N_{\rm eff}} \Omega \tau \right). $ [Preview Abstract] |
Thursday, June 7, 2007 3:42PM - 3:54PM |
J5.00012: Quantum electrodynamics of qubits Iwo Bialynicki-Birula, Tomasz Sowinski Powerful methods of relativistic quantum electrodynamics are applied to the study of the interaction of qubits with the quantized electromagnetic field. These methods lead to a significant progress in the study of various properties of two-level systems. The application of the tools of relativistic QED to the description of two-level system is made possible by a close analogy between the Dirac sea of filled negative-energy electron states and the occupied lower-energy state of a two-level system. Propagators, the S-matrix, and Feynman diagrams turn out to be particularly useful. In applying these tools we profit from numerous simplifications in the calculations that made the Feynman-Schwinger-Dyson approach to QED so successful. Owing to these simplifications, the calculations of higher order corrections in perturbation theory become very simple. The integration over the intermediate energies can be performed in any order of perturbation theory by the standard method of residues. The analysis is carried out for two-level atoms and for spins. In particular, the polarizability of a two-level atom is calculated in the fourth-order of perturbation theory. This calculation is made simple by the analogy with the vacuum polarization in QED. Also, the treatment of nonlinear phenomena in two-level systems by analogy with their counterparts in QED is very successful. [Preview Abstract] |
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