Abstract
The absorption of traveling photons resonant with electric dipole transitions of an atomic gas naturally leads to electric dipole spin wave excitations. For a number of applications, it would be highly desirable to shape and coherently control the spatial waveform of the spin waves before spontaneous emission can occur. This paper details a recently developed optical control technique to achieve this goal, where counter-propagating, shaped sub-nanosecond pulses impart sub-wavelength geometric phases to the spin waves by cyclically driving an auxiliary transition. In particular, we apply this technique to reversibly shift the wave vector of a spin wave on the $D2$ line of laser-cooled $^{87}$Rb atoms, by driving an auxiliary $D1$ transition with shape-optimized pulses, so as to shut off and recall superradiance on demand. We investigate a spin-dependent momentum transfer during the spin-wave control process, which leads to a transient optical force as large as $\sim 1\hbar k$/ns, and study the limitations to the achieved $70\sim 75\%$ spin wave control efficiency by jointly characterizing the spin-wave control and matterwave acceleration. Aided by numerical modeling, we project potential future improvements of the control fidelity to the $99\%$ level when the atomic states are better prepared and by equipping a faster and more powerful pulse shaper. Our technique also enables a background-free measurement of the superradiant emission to unveil the precise scaling of the emission intensity and decay rate with optical depth.
Highlights
Spontaneous emission is typically a decoherence effect to avoid when levels in small quantum systems are chosen to encode information for, e.g., quantum computation, simulation, or sensing [1,2,3,4]
Instead of using ultrafast lasers, here we develop a wide-band pulse-shaping technique based on fiber-based sideband electro-optical modulation of a cw laser [30], with up to 13 GHz modulation bandwidth, to support the flexibly programmable error-resilient spin wave control
Compared with previous work on spectroscopy based upon perturbative nonlinear optical effects [41,42,43], our technique is unique in that we steer the atomic state over the entire Bloch sphere of the two-level system to achieve the geometric robustness toward perfect spin-wave control set by Eq (2)
Summary
Spontaneous emission is typically a decoherence effect to avoid when levels in small quantum systems are chosen to encode information for, e.g., quantum computation, simulation, or sensing [1,2,3,4]. What is needed is a technique to efficiently and coherently alter the phase-matching condition of collective atomic excitations in the temporal domain—that is, to modify the wave vector of the spin waves and coherently convert between superradiant and subradiant modes—on rapid timescales faster than the typical emission time of atoms themselves. We exploit the ability to shift the dipole spin-wave vector to measure phase-matched forward collective emission in a background-free manner. To ensure completeness and to provide better context, key ideas from Ref. [30] are repeated in this paper
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
