# Atomic Physics Seminar

The number of atoms in the trap is random and is commonly described by the Poissonian statistics. In the regime of Rydberg blockade an atomic ensemble, which consists of N atoms, can be treated as a two-level system with enhanced coupling to the laser radiation field by a factor of compared to a single atom. A single Rydberg excitation is shared between all atoms in the ensemble. Fluctuations of the frequency of Rabi oscillations between the collective states of the atomic ensembles can result in collapses and revivals of Rabi oscillations, similarly to Jaynes-Cummings model in quantum optics. These fluctuations can also lead to significant errors in quantum information processing. We have proposed to use the adiabatic passage in atomic ensembles for deterministic single-atom excitation and quantum logic gates in ensembles with unknown numbers of atoms. The double adiabatic sequences provide deterministic single-atom Rydberg excitation and remove the accumulation of undesirable dynamic phase. This can be used to implement quantum gates on collectively encoded qubits without precise knowledge of N.

*Rzhanov Institute of Semiconductor Physics :Novosibirsk State University: Novosibirsk, Russia*

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TBD

*University of Calgary*

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*Korea University*

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Trapped, cold Rydberg atoms are important in future applications in high-precision measurement, field sensing and quantum information processing. The following topics will be discussed. (1) We use high-resolution atom imaging to measure the Rydberg-Rydberg correlation function in Rydberg-atom samples prepared within the spatially-varying light shifts of a laser trap. We study the pair-correlation behavior as well as direct two-photon excitation of correlated Rydberg-atom pairs in the trap. (2) We employ a standing-wave laser trap in combination with Rydberg-atom position control within the standing wave to show that optical photoionization of a Rydberg atom does not occur within the main lobes of the Rydberg electron’s wave-function, but only within a relatively small volume around the nucleus. This evidence is consistent with the (sometimes unexpected) validity of the electric-dipole approximation for optical Rydberg-atom photoionization. (3) Modulated, spatially inhomogeneous light fields, such as amplitude-modulated optical lattices, can be used to drive multipole microwave transitions between Rydberg levels in a minimally invasive manner. This enables high-precision measurements of atomic properties. I will show first results with this new type of spectroscopy. (4) High-precision spectroscopy will be most promising with circular, Bohr-like Rydberg states. These have long lifetimes and low electric polarizabilities, among other nice features. Towards this, we have recently produced and trapped such atoms with an adiabatic “crossed-fields” state-switching method. Looking ahead, I will briefly discuss how these methods could be combined to perform specific high-precision measurements.

*University of Michigan*

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Originally inhomegeneities, decoherence and decay of the atomic systems were minimized in quantum computing proposals so that their effects would not disturb the ideal unitary evolution of the system. Recent works, however, suggest a quite opposite strategy, where inhomegeneities are created on purpose and the system is driven on resonance with short lived states such that it dephases and decays to robust steady states. By suitable use of the interactions, these states can be selected, e.g., as entangled states or states encoding the outcome of a quantum computation. We investigate the coherent effects induced by dissipation and decoherence in neutral atom based quantum computing proposals, for creating robust entangled states and long distance gates.

*Aarhus University, Denmark*

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We present our progress on the coherent control and investigation of Rydberg atoms in small vapor cells. We show that we are able to drive Rabi oscillations on the nanosecond timescale to a Rydberg state by using a pulsed laser excitation and are therefore faster than the coherence time limitation given by the Doppler width [2].<br><br>

A systematic investigation of the dephasing of these oscillations for different atomic densities and Rydberg S-states (n = 22-40) reveals a clear signature for Rydberg-Rydberg interaction which is the basis for quantum devices based on the Rydberg blockade. Due to the high excitation bandwidth we are probing interaction level shifts up to a few GHz which correspond to very small interatomic distances (&lt; 1μm). Despite the complicated level structure for Rydberg molecular states at these distances we find that the scaling with principle quantum number is still consistent with van der Waals type interaction. The strength of the interaction exceeds the energy scale of thermal motion (i.e. the Doppler broadening) and therefore enables strong quantum correlations above room temperature [3].<br><br>

Furthermore we present our latest results on the combination of the pulsed Rydberg excitation with a four-wave-mixing scheme [4] and our progress towards the creation of non-classical light. <br><br>

[1] M. Saffman et al., RMP 82, 2313 (2010) and references therein <br><br>

[2] B. Huber et al., PRL 107, 243001 (2011) <br><br>

[3] T. Baluktsian et al., PRL 110, 123001 (2013)<br><br>

[4] M. Saffman and T. G. Walker, Phys. Rev. A 66, 065403 (2002), M. M. Müller, et al. Phys. Rev. A 87, 053412 (2013)<br><br>

*University of Stuttgart*

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The Standard Model and General Relativity have proven to be extraordinarily good at describing the world we live in. Unfortunately, it is not yet clear how these theories are reconciled with one another at extremely high energies. This is one of the puzzles which motivates ongoing experimental and observational searches for new phenomena in high energy, astro-particle, gravitational, and precision measurement physics. Any deviation from the predictions of the Standard Model and General Relativity could point the way towards a unified theory. This talk will describe recent developments in precision tests of the fundamental symmetries underlying both the Standard Model and General Relativity using atomic physics techniques. As I will show, sometimes the most sensitive test of new physics doesn't require observing physics at very high energies, large distances, or extreme gravitational environments. Sometimes the best place to look for extraordinary physics is in what might at first seem to be a rather ordinary place.

*UC Berkeley*

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We propose a quantum interface for creating hybrid entanglement between neutral atom and superconducting qubits. The interface is mediated by coupling superconducting qubits to microwaves, and microwaves to Rydberg excited single atoms. Fidelity calculations based on realistic parameters for an atom located close to a CPW microwave resonator, and a progress report on experimental implementation will be presented.

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We will present a discussion of quantum spin ice, which represents a paradigmatic example on how the physics of frustrated magnets is related to gauge theories. The goal is to assemble a system of cold Rydberg atoms and to design interactions that realize a toy model of quantum spin ice on a two-dimensional checkerboard lattice. In particular, we exploit the strong angular dependence of Van-der-Waals interactions between high angular momentum Rydberg states. Together with the possibility of designing step-like potentials using ground state atoms weakly dressed by Rydberg states, we can implement Abelian gauge theories in a series of geometries, which could be demonstrated within state of the art experiments.

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Electromagnetically induced transparency (EIT) is essential in coherent atomic physics, which has been extensively studied in the last two decades. The important properties of EIT are its steep normal linear dispersion and greatly enhanced nonlinearity with a negligible absorption near atomic resonance. When EIT medium is placed inside an optical cavity, many interesting effects can occur. In this talk, I will discuss several experiments in EIT-related atom-cavity systems. Particular attention will be given to nonlinear optical cavity transmission spectra and optical multistate switching with Doppler-broadened multilevel atoms inside an optical ring cavity. In addition, parity-time symmetry and optically induced lattice in EIT-related medium will be briefly discussed.

*University of Arkansas*

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