K. Salit

Demonstration of a tunable-bandwidth white-light interferometer using anomalous dispersion in atomic vapor.

Recently, the design of a white-light cavity has been proposed using negative dispersion in an intracavity medium to make the cavity resonate over a large range of frequencies and still maintain a high cavity buildup. This Letter presents the first demonstration of this effect in a free-space cavity. The negative dispersion of the intracavity medium is caused by bifrequency Raman gain in an atomic vapor cell. A significantly broad cavity response over a bandwidth greater than 20 MHz has been observed. A key application of this device would be in enhancing the sensitivity-bandwidth product of the next generation gravitational wave detectors that make use of the so-called signal-recycling mirror.

Superluminal ring laser for hypersensitive sensing

The group velocity of light becomes superluminal in a medium with a tuned negative dispersion, using two gain peaks, for example. Inside a laser, however, the gain is constant, equaling the loss. We show here that the effective dispersion experienced by the lasing frequency is still sensitive to the spectral profile of the unsaturated gain. In particular, a dip in the gain profile leads to a superluminal group velocity for the lasing mode. The displacement sensitivity of the lasing frequency is enhanced by nearly five orders of magnitude, leading to a versatile sensor of hyper sensitivity.

Fast-light for astrophysics: super-sensitive gyroscopes and gravitational wave detectors

We present a theoretical analysis and experimental study of the behaviour of optical cavities filled with slow- and fast-light materials, and show that the fast-light material-filled cavities, which can function as ‘white light cavities’, have properties useful for astrophysical applications such as enhancing the sensitivity-bandwidth product of gravitational wave detection and terrestrial measurement of Lense–Thirring rotation via precision gyroscopy.

Simultaneous slow and fast light effects using probe gain and pump depletion via Raman gain in atomic vapor

We demonstrate experimentally slow and fast light effects achieved simultaneously using Raman gain and pump depletion in an atomic vapor. Heterodyne phase measurements show opposite dispersion characteristics at the pump and probe frequencies. Optical pulse propagations in the vapor medium confirm the slow and fast light effects due to these dispersions. We discuss applications of this technique in recently proposed rotation sensing and broadband detection schemes.

Ultra-low power, Zeno effect based optical modulation in a degenerate V-system with a tapered nano fiber in atomic vapor

We demonstrate an ultra-low light level optical modulator using a tapered nano fiber embedded in a hot rubidium vapor. The control and signal beams are co-propagating but orthogonally polarized, leading to a degenerate V-system involving coherent superpositions of Zeeman sublevels. The modulation is due primarily to the quantum Zeno effect for the signal beam induced by the control beam. For a control power of 40 nW and a signal power of 100 pW, we observe near 100% modulation. The ultra-low power level needed for the modulation is due to a combination of the Zeno effect and the extreme field localization in the evanescent field around the taper.

Quantum communication and computing with atomic ensembles using a light-shift-imbalance-induced blockade

Recently, we have shown that for conditions under which the so-called light-shift imbalance induced blockade occurs, the collective excitation of an ensemble of a multilevel atom can be treated as a closed two-level system. In this paper, we describe how such a system can be used as a quantum bit (qubit) for quantum communication and quantum computing. Specifically, we show how to realize a controlled-NOT gate using the collective qubit and an easily accessible ring cavity, via an extension of the so-called Pellizzari scheme. We also describe how multiple, small-scale quantum computers realized using these qubits can be linked effectively for implementing a quantum internet. We describe the details of the energy levels and transitions in an

Light-shift imbalance induced blockade of collective excitations beyond the lowest order

^{87}\mathrm{Rb}

Controllable anomalous dispersion and group index nulling via bi-frequency Raman gain for ultraprecision rotation sensing

atom that could be used for implementing these schemes.

Ultra-precise rotation sensing with a superluminal ring laser

Current proposals focusing on neutral atoms for quantum computing are mostly based on using single atoms as quantum bits (qubits), while using cavity induced coupling or dipole–dipole interaction for two-qubit operations. An alternative approach is to use atomic ensembles as quantum bits. However, when an atomic ensemble is excited, by a laser beam matched to a two-level transition (or a Raman transition) for example, it leads to a cascade of many states as more and more photons are absorbed [R.H. Dicke, Phys. Rev. 93 (1954) 99]. In order to make use of an ensemble as a qubit, it is necessary to disrupt this cascade, and restrict the excitation to the absorption (and emission) of a single photon only. Here, we show how this can be achieved by using a new type of blockade mechanism, based on the light-shift imbalance (LSI) in a Raman transition. We describe first a simple example illustrating the concept of light-shift imbalance induced blockade (LSIIB) using a multi-level structure in a single atom, and show verifications of the analytic prediction using numerical simulations. We then extend this model to show how a blockade can be realized by using LSI in the excitation of an ensemble. Specifically, we show how the LSIIB process enables one to treat the ensemble as a two-level atom that undergoes fully deterministic Rabi oscillations between two collective quantum states, while suppressing excitations of higher order collective states.

Raman resonant probe gain and pump depletion in rubidium vapor for simultaneous slow and fast light effects

Using a bi-frequency pumped Raman amplifier in a Rb vapor cell, we demonstrate experimentally the condition for achieving a null group index, necessary for fast-light enhanced rotation sensing in a passive cavity Sagnac gyroscope.