AtMol Research Seminar Archive
Index Current Seminars

Epiphany 2011

Date Speaker Institution
Orbital excitation blockade and algorithmic cooling in quantum gases (Journal Club Talk)
18th January Mr. John Helm University of Durham

I will speak on the subject of recent work done in the Greiner lab, Harvard. The work covers a new blockade effect dubbed as the orbital excitation blockade (OEB) and its applications to algorithmic cooling. I will also describe the experimental setup used to image these systems, which is capable of imaging single atoms by resolving individual lattice sites on the scale of ~600nm

The world through a rotating window - Enhancing the rotation image drag in a slow light medium
25th January Dr. Sonja Franke-Arnold University of Glasgow

Since at least a century, researchers have been concerned with the fact whether light may be dragged along by a medium (be it water, glass or ether). A spinning medium rotates the polarisation (by typically a microradian), but the same mechamism has been predicted to also rotate an image. By slowing down light to about the speed of sound we managed to enhance this effect and observed a macroscopic rotation of a light profile. This effect may be interesting for delay and storage of quantum images. As an aside, I'll also mention our very recent results on frequency shifting light carrying orbital angular momentum via four-wave mixing in a Rubidium vapour.

Coupling persistent current loops to defects in diamond (Journal Club Talk)
1st February Mr. Christophe Vaillant University of Durham

Superconducting flux qubits have shown great promise for future implementation of quantum computers, however remain limited by their short coherence times. Hybrid systems hope to avoid this by coupling to longer lived atomic states, and such a hybrid system has recently been demonstrated in an electron spin ensemble in diamond. In this talk I will go through some of the basic concepts of superconducting flux qubits as well as nitrogen vacancy centres in diamond, and present the results of the recent experiment that coherently coupled the two.

Observing the Average Trajectories of Single Photons in a Two-Slit Interferometer (Journal Club Talk)
8th February Ms. Danielle Boddy University of Durham

A consequence of the uncertainty principle is that one may not discuss the trajectory that a quantum particle takes, because any measurement of the position irrevocably disturbs the momentum, and vice versa. Using weak measurements, however, it is possible to define a set of trajectories for an ensemble of quantum particles. In this talk I will go through some of the basic concepts of quantum theory, as well as introduce the idea of a weak measurement, and present the results of the experiment.

Interaction-based quantum metrology showing scaling beyond the Heisenberg limit
15th February Mr. David Paredes University of Durham

An interferometer using N independent particles to measure a parameter "O" can achieve at best the standard quantum limit of sensitivity, δ O ∝ N^(-1/2). However, using N entangled particles and exotic states, such an interferometer can in principle achieve the Heisenberg limit, δ O ∝ N^(-1). Recently, it has been shown that interactions amongst particles allow (in principle) scaling beyond the Heisenberg limit. In this work, super-Heisenberg scaling is achieved in the measurement of the magnetization of an atomic ensemble.

Matter-wave amplification in a seeded 23Na spinor Bose-Einstein condensate
22nd February Dr. Paul Griffin University of Strathclyde

In a spinor Bose-Einstein condensate the atoms can be in a superposition of internal quantum states. Thus, a BEC of spin-1 particles, like the F = 1 ground state of Na atoms, can be thought of as being a single condensate with the atoms in a superposition of the three spin projections mF = -1, 0, and +1, or equivalently, the superposition of three coupled BECs with the same spatial wavefunction, one in each of these spin states.

I will report on the spinor BEC experiment in Na atoms at NIST, Gaithersburg. Here we use microwave-dressing to create a nonlinear matter-wave amplifier that can be used to produce spin-squeezed states. We examine weak coherent seeds and show that the populations distribution after an evolution time can be used as a large amplitude measurement initial seed. This kind of measurement may be important in achieving high phase sensitivity in Heisenberg-limited matter-wave interferometers.

The Bose-Einstein Condensate in Semiconductor Microcavities
29th February (1 PM) Prof. Maurice Skolnick University of Sheffield

Probing correlated quantum systems with single-atom resolution
29th February (4 PM) Prof. Stefan Kuhr University of Strathclyde

Ultracold atoms in optical lattices are a versatile tool to investigate fundamental properties of quantum many body systems. We demonstrate how the control of such systems can be extended down to the most fundamental level of single atomic spins at specific lattice sites. Using a high-resolution optical imaging system, we were able to obtain fluorescence images of strongly interacting bosonic Mott insulators with single-atom and single-site resolution [1] and addressed the atomic spins with sub-diffraction-limited resolution [2]. In addition, we directly monitored the tunneling quantum dynamics of single atoms in the lattice, and observed quantum-correlated particle-hole pairs [3] and spreading of correlations after a parameter quench [4], and the quantum dynamics of spin-impurities. Our results open the path to a wide range of novel applications from observation of entropy transport, implementation of novel cooling schemes, and engineering of quantum many-body phases to quantum information processing.

[1] J. F. Sherson, C. Weitenberg, M. Endres, M. Cheneau, I. Bloch, S. Kuhr, Single-atom-resolved fluorescence imaging of an atomic Mott insulator, Nature 467, 68 (2010).

[2] C. Weitenberg, M. Endres, J. F. Sherson, M. Cheneau, P. Schauß, T. Fukuhara, I.Bloch, S. Kuhr, Single-spin addressing in an atomic Mott insulator, Nature 471, 319 (2011).

[3] M. Endres, M. Cheneau, T. Fukuhara, C. Weitenberg, P. Schauß, C. Gross, L. Mazza, M.C. Banuls, L. Pollet, I. Bloch, S. Kuhr, Observation of Correlated Particle-Hole Pairs and String Order in Low-Dimensional Mott Insulators, Science 334, 200 (2011).

[4] M. Cheneau, P. Barmettler, D. Poletti, M. Endres, P. Schauß, T. Fukuhara, C. Gross, I. Bloch, C. Kollath, S. Kuhr, Light-cone-like spreading of correlations in a quantum many-body system, Nature 481, 484 (2012).

Coherent Quantum Control of Phosphorus Donor Rydberg States in Silicon using THz Laser Pulses
7th March Dr. Stephen Lynch University of Cardiff

Crystalline silicon can be conveniently doped by substituting a small number of silicon atoms at lattice sites with atoms from the adjacent pnictogen group-V column of the periodic table. At room temperature this results in an excess of free electrons and the material is n-doped. At low temperatures the extra electron left over after bonding remains loosely bound to the positive core. This object looks and behaves like an isolated hydrogen atom. There is an analogous Rydberg series of narrow lines in the absorption spectrum but it is down shifted towards much lower energies. Whereas the Rydberg series for hydrogen lies in the visible band, the corresponding series for the hydrogen-like donor lies in the THz band.

14th March (Board of Examiners)

Optically driven Rydberg gases and Rydberg polaritons
21st March Prof. Michael Fleischhauer Technische Universität Kaiserslautern

Resonantly driven Rydberg gases can most conveniently be described in terms of slow-light polaritons. They are subject to a strong and non-local interaction mediated by a van-der Waals coupling between excited Rydberg atoms. I will present and discuss an effective many-body model for these Rydberg polaritons characterized by a power-law interaction for large separations and a dissipative blockade phenomenon for small interparticle distances. The non-local effective interaction gives rize to interesting many-body phenomena such as the generation of photons with an avoided volume, visible in stronlgy suppressed two-particle correlations inside the blockade volume. I will argue that the latter effect is essential for explaining recent experiments on light propagation in Rydberg gases. The long-range interaction can moreover give rize to the formation of quasi-crystalline structures of photons. In a one dimensional system the low-energy dynamics of the polaritons can be described in terms of a Luttinger liquid model. The relevant parameter are obtained by DMRG simulations and the conditions for the formation of crystalline order are discussed. Furthermore an alternative approach to create orderd structures of Rydberg excitations by steady-state optical pumping is presented. A corresponding Liouville operator for the many-body system is derived and solved in the steady state.