D. D. Yavuz

Observation of Rydberg blockade between two atoms

When two single Rydberg atoms—those having electrons in highly excited states—interact, one can be used to control the quantum state of the other. Two independent experiments now demonstrate a ‘Rydberg blockade’, an effect that might make long-range quantum gates between neutral atoms possible. Blockade interactions whereby a single particle prevents the flow or excitation of other particles provide a mechanism for control of quantum states, including entanglement of two or more particles. Blockade has been observed for electrons1,2,3, photons4 and cold atoms5. Furthermore, dipolar interactions between highly excited atoms have been proposed as a mechanism for ‘Rydberg blockade’6,7, which might provide a novel approach to a number of quantum protocols8,9,10,11. Dipolar interactions between Rydberg atoms were observed several decades ago12 and have been studied recently in a many-body regime using cold atoms13,14,15,16,17,18. However, to harness Rydberg blockade for controlled quantum dynamics, it is necessary to achieve strong interactions between single pairs of atoms. Here, we demonstrate that a single Rydberg-excited rubidium atom blocks excitation of a second atom located more than 10 μm away. The observed probability of double excitation is less than 20%, consistent with a theoretical model of the Rydberg interaction augmented by Monte Carlo simulations that account for experimental imperfections.

Fast Ground State Manipulation of Neutral Atoms in Microscopic Optical Traps

We demonstrate Rabi flopping at MHz rates between ground hyperfine states of neutral 87Rb atoms that are trapped in two micron sized optical traps. Using tightly focused laser beams we demonstrate high fidelity, site specific Rabi rotations with cross talk on neighboring sites separated by 8 microm at the level of 10(-3). Ramsey spectroscopy is used to measure a dephasing time of 870 micros, which is approximately 5000 longer than the time for a pi/2 pulse.

Rabi oscillations between ground and Rydberg states with dipole-dipole atomic interactions

We demonstrate Rabi oscillations of small numbers of 87Rb atoms between ground and Rydberg states with n< or =43. Coherent population oscillations are observed for single atoms, while the presence of two or more atoms decoheres the oscillations. We show that these observations are consistent with van der Waals interactions of Rydberg atoms.

Generation and control of femtosecond pulses by molecular modulation

We have demonstrated that coherent molecular modulation can result in the collinear generation of mutually-coherent spectral sidebands that extend in frequency from the infrared to the far ultraviolet. Our technique is based on adiabatic preparation of a highly coherent molecular superposition-state, which is achieved by using narrow-linewidth lasers slightly detuned from a Raman resonance. The phases of the resultant Stokes and anti-Stokes sidebands are adjusted in order to synthesize desired single-cycle pulse trains at the target. In this article we review recent improvements and developments in this area, including: techniques for increasing the number of generated sidebands; synchronization of the pulse trains with the molecular motion in the given molecular system; laser self-focusing and spatial soliton formation due to the coherent interaction of light with oscillating molecules. In the future, this Raman source may produce sub-cycle optical pulses, and allow synthesis of waveforms where the electric field is a predetermined function of time, not limited to a quasi-sinusoidal oscillation.

Subfemtosecond pulse generation by rotational molecular modulation

We extend a recent suggestion for the generation of subfemtosecond pulses by molecular modulation [Phys. Rev. Lett. 81, 2894 (1998)] to the rotational spectrum of molecular hydrogen (H(2)) . When a rotational transition |a? ? |b? is strongly driven (|rho(ab) |=0.5) the generation and phase-slip lengths are of the same order and the Raman spectrum has approximately Bessel function sideband amplitudes. Numerical simulation predicts that this spectrum (generated in a 14-cm-long cell at 1-atm pressure of H(2)) will compress into a train of pulses with 94-fs pulse separation and a pulse length of 0.5 fs.

Refractive Index Enhancement with Vanishing Absorption in an Atomic Vapor

We report a proof-of-principle experiment where the refractive index of an atomic vapor is enhanced while maintaining vanishing absorption of the beam. The key idea is to drive alkali atoms in a vapor with appropriate control lasers and induce a gain resonance and an absorption resonance for a probe beam in a two-photon Raman configuration. The strength and the position of these two resonances can be manipulated by changing the parameters of the control lasers. By using the interference between these two resonances, we obtain an enhanced refractive index without an increase in the absorption.

Rotational Raman generation with near-unity conversion efficiency

We demonstrate collinear generation of equidistant rotational sidebands in low-pressure molecular hydrogen with near-unity conversion efficiency. The spectrum consists of 37 coherent sidebands covering over 20, 000 cm(-1) of spectral bandwidth and ranging from 1.37mum to 352 nm in wavelength.

Generation of a single-cycle optical pulse

By electronically adjusting the phases of seven Raman sidebands which span 1.56 µm to 410 nm we generate a train rain of well-formed single-cycle optical pulses with a pulse width of 1.5 fs.

Nearly copropagating sheared laser pulse FEL undulator for soft x-rays

A conceptual design for a soft x-ray free-electron laser (FEL) using a short-pulsed, high energy near infrared laser undulator and a low-emittance modest-energy (?170?MeV) electron beam is described. This low-cost design uses the laser undulator beam in a nearly copropagating fashion with respect to the electron beam, instead of the traditional ?head-on? fashion. The nearly copropagating geometry reduces the Doppler shift of scattered radiation to yield soft, rather than hard x-rays. To increase the FEL gain a sheared laser pulse from a Ti?:?sapphire or other broadband laser is used to extend the otherwise short interaction time of the nearly copropagating laser undulator beam with a relativistic electron beam.

Continuous-wave high-power rotational Raman generation in molecular deuterium

We report the generation of more than 300 mW of rotational Stokes output power in a CW Raman laser. The generation is achieved in low-pressure molecular deuterium inside a high-finesse cavity.