J. D. Pritchard

Cooperative atom-light interaction in a blockaded Rydberg ensemble

By coupling a probe transition to a Rydberg state using electromagnetically induced transparency (EIT) we map the strong dipole-dipole interactions onto an optical field. We characterize the resulting cooperative optical nonlinearity as a function of probe strength and density. We demonstrate good quantitative agreement between the experiment and an N-atom cooperative model for N=3 atoms per blockade sphere and the n=60 Rydberg state. The measured linewidth of the EIT resonance places an upper limit on the dephasing rate of the blockade spheres of <110 kHz.We demonstrate a cooperative optical non-linearity caused by dipolar interactions between Rydberg atoms in an ultra-cold atomic ensemble. By coupling a probe transition to the Rydberg state we map the strong dipoledipole interactions between Rydberg pairs onto the optical field. We characterize the non-linearity as a function of electric field and density, and demonstrate the enhancement of the optical non-linearity due to cooperativity.

Storage and control of optical photons using Rydberg polaritons.

We use a microwave field to control the quantum state of optical photons stored in a cold atomic cloud. The photons are stored in highly excited collective states (Rydberg polaritons) enabling both fast qubit rotations and control of photon-photon interactions. Through the collective read-out of these pseudospin rotations it is shown that the microwave field modifies the long-range interactions between polaritons. This technique provides a powerful interface between the microwave and optical domains, with applications in quantum simulations of spin liquids, quantum metrology and quantum networks.

Laser frequency stabilization to excited state transitions using electromagnetically induced transparency in a cascade system

We demonstrate laser frequency stabilization to excited state transitions using cascade electromagnetically induced transparency. Using a room temperature Rb vapor cell as a reference, we stabilize a first diode laser to the D2 transition and a second laser to a transition from the intermediate 5P3/2 state to a highly excited state with principal quantum number n=19–70. A combined laser linewidth of 280±50 kHz over a 100 μs time period is achieved. This method may be applied generally to any cascade system and allows laser stabilization to an atomic reference in the absence of a direct absorption signal.

Nonlinear optics using cold Rydberg atoms

The implementation of electromagnetically induced transparency (EIT) in a cold Rydberg gas provides an attractive route towards strong photon--photon interactions and fully deterministic all-optical quantum information processing. In this brief review we discuss the underlying principles of how large single photon non-linearities are achieved in this system and describe experimental progress to date.

Electromagnetically induced transparency of an interacting cold Rydberg ensemble

We study electromagnetically induced transparency (EIT) of a weakly interacting cold Rydberg gas. We show that for Rydberg states with principal quantum numbers in the range n = 19–26, the onset of interactions is manifest as a depopulation of the Rydberg state. In the limit of a weak probe where the depopulation effect is negligible, we observe no evidence of interaction-induced decoherence and obtain a narrow Rydberg dark resonance with a linewidth of <600 kHz.

Quantum interference in interacting three-level Rydberg gases : coherent population trapping and electromagnetically induced transparency

In this paper, we consider the effects of strong dipole-dipole interactions on three-level interference phenomena such as coherent population trapping and electromagnetically induced transparency. Experiments are performed on laser cooled rubidium atoms and the results compared to a many-body theory based on either a reduced many-body density matrix expansion or Monte Carlo simulations of many-body rate equations. We show that these approaches permit quantitative predictions of the experimentally observed excitation and transmission spectra. Based on the calculations, we moreover predict a universal scaling of the nonlinear response of cold Rydberg gases.

Microwave dressing of Rydberg dark states

We study electromagnetically induced transparency (EIT) in the 5s→5p→46s ladder system of a cold 87Rb gas. We show that the resonant microwave coupling between the 46s and 45p states leads to an Autler–Townes splitting of the EIT resonance. This splitting can be employed to vary the group index by ±105 allowing independent control of the propagation of dark state polaritons. We also demonstrate that microwave dressing leads to enhanced interaction effects. In particular, we present evidence for a 1/R3 energy shift between Rydberg states resonantly coupled by the microwave field and the ensuing breakdown of the pairwise interaction approximation.

Hybrid atom-photon quantum gate in a superconducting microwave resonator

We propose a hybrid quantum gate between an atom and a microwave photon in a superconducting coplanar waveguide cavity by exploiting the strong resonant microwave coupling between adjacent Rydberg states. Using experimentally achievable parameters gate fidelities >0.99 are possible on submicrosecond time scales for waveguide temperatures below 40 mK. This provides a mechanism for generating entanglement between two disparate quantum systems and represents an important step in the creation of a hybrid quantum interface applicable for both quantum simulation and quantum information processing.

ARC : an open-source library for calculating properties of alkali Rydberg atoms.

Abstract We present an object-oriented Python library for the computation of properties of highly-excited Rydberg states of alkali atoms. These include single-body effects such as dipole matrix elements, excited-state lifetimes (radiative and black-body limited) and Stark maps of atoms in external electric fields, as well as two-atom interaction potentials accounting for dipole and quadrupole coupling effects valid at both long and short range for arbitrary placement of the atomic dipoles. The package is cross-referenced to precise measurements of atomic energy levels and features extensive documentation to facilitate rapid upgrade or expansion by users. This library has direct application in the field of quantum information and quantum optics which exploit the strong Rydberg dipolar interactions for two-qubit gates, robust atom-light interfaces and simulating quantum many-body physics, as well as the field of metrology using Rydberg atoms as precise microwave electrometers. Program summary Program Title: ARC: Alkali Rydberg Calculator Program Files doi: http://dx.doi.org/10.17632/hm5n8w628c.1 Licensing provisions: BSD-3-Clause Programming language: Python 2.7 or 3.5, with C extension External Routines: NumPy [1], SciPy [1], Matplotlib [2] Nature of problem: Calculating atomic properties of alkali atoms including lifetimes, energies, Stark shifts and dipole–dipole interaction strengths using matrix elements evaluated from radial wavefunctions. Solution method: Numerical integration of radial Schrodinger equation to obtain atomic wavefunctions, which are then used to evaluate dipole matrix elements. Properties are calculated using second order perturbation theory or exact diagonalisation of the interaction Hamiltonian, yielding results valid even at large external fields or small interatomic separation. Restrictions: External electric field fixed to be parallel to quantisation axis. Supplementary material: Detailed documentation (.html), and Jupyter notebook with examples and benchmarking runs (.html and .ipynb). [1] T.E. Oliphant, Comput. Sci. Eng. 9, 10 (2007). http://www.scipy.org/ . [2] J.D. Hunter, Comput. Sci. Eng. 9, 90 (2007). http://matplotlib.org/ .

Demonstration of an inductively coupled ring trap for cold atoms

We report the first demonstration of an inductively coupled magnetic ring trap for cold atoms. A uniform, ac magnetic field is used to induce current in a copper ring, which creates an opposing magnetic field that is time-averaged to produce a smooth cylindrically symmetric ring trap of radius 5 mm. We use a laser-cooled atomic sample to characterize the loading efficiency and adiabaticity of the magnetic potential, achieving a vacuum-limited lifetime in the trap. This technique is suitable for creating scalable toroidal waveguides for applications in matter-wave interferometry, offering long interaction times and large enclosed areas.