Christopher P. Search

Ultra-sensitive chip scale Sagnac gyroscope based on periodically modulated coupling of a coupled resonator optical waveguide

We analyze the sensitivity to inertial rotations Ω of a micron scale integrated gyroscope consisting of a coupled resonator optical waveguide (CROW). We show here that by periodic modulation of the evanescent coupling between resonators, the sensitivity to rotations can be enhanced by a factor up to 10(9) in comparison to a conventional CROW with uniform coupling between resonators. Moreover, the overall shape of the transmission through this CROW superlattice is qualitatively changed resulting in a single sharp transmission resonance located at Ω = 0s-1 instead of a broad transmission band. The modulated coupling therefore allows the CROW gyroscope to operate without phase biasing and with sensitivities suitable for inertial navigation even with the inclusion of resonator losses.

Spin waves in a Bose-Einstein--condensed atomic spin chain.

The spin dynamics of atomic Bose-Einstein condensates confined in a one-dimensional optical lattice is studied. The condensates at each lattice site behave like spin magnets that can interact with each other through both the light-induced dipole-dipole interaction and the static magnetic dipole-dipole interaction. We show how these site-to-site dipolar interactions can distort the ground-state spin orientations and lead to the excitation of spin waves. The dispersion relation of the spin waves is studied and possible detection schemes are proposed.

Chirped area coupled resonator optical waveguide gyroscope

We study the transmission of an optical field through a rotating coupled resonator optical waveguide (CROW) in which the size of the ring resonators changes from one ring to the next. We focus on symmetric integer wavelength chirps of the circumference of the rings relative to the central ring in the array. The transfer matrix method is used to obtain the transmission as a function of the inertial rotation rate Ω resulting from the Sagnac effect. Chirping increases the slope of the oscillations in the transmission as a function of Ω, which can be exploited to further enhance the rotation sensitivity beyond that of a CROW with uniform resonators.

Suppression of magnetic state decoherence using ultrafast optical pulses

It is shown that magnetic state decoherence produced by collisions in a thermal vapor can be suppressed by the application of a train of ultrafast optical pulses.

Effect of input–output coupling on the sensitivity of coupled resonator optical waveguide gyroscopes

We analyze how the evanescent coupling, κe, between the outermost resonators and input/output waveguides of an N-resonator coupled resonator optical waveguide (CROW) gyroscope affects the transmission and sensitivity to rotations. For constant coupling between resonators κ, rotation sensitivities increase as both κe→0 and κe→1 while between these two limits the sensitivity has a minimum. In the weak coupling regime, κe→0, the sensitivity is enhanced by Fabry–Perot oscillations due to the impedance mismatch at the input/output waveguide–CROW interface, while in the strong coupling regime, κe→1, the sensitivity is reduced because the outermost resonators no longer contribute to the CROW transmission. For small N the sensitivity is proportional to N2, while at larger N the sensitivity begins to decrease due to resonator losses.

Spin current and shot noise from a quantum dot coupled to a quantized cavity field

We examine the spin current and the associated shot noise generated in a quantum dot connected to normal leads with zero bias voltage across the dot. The spin current is generated by spin flip transitions induced by a quantized electromagnetic field inside a cavity with one of the Zeeman states lying below the Fermi level of the leads and the other above. In the limit of strong Coulomb blockade, this model is analogous to the Jaynes-Cummings model in quantum optics. We also calculate the photon current and photon current shot noise resulting from photons leaking out of the cavity. We show that the photon current is equal to the spin current and that the spin current can be significantly larger than for the case of a classical driving field as a result of cavity losses. In addition to this, the frequency-dependent spin (photon) current shot noise show dips (peaks) that are a result of the discrete nature of photons.

Effect of resonator losses on the sensitivity of coupled resonator optical waveguide gyroscopes

Recently there has been a growing interest in microphotonic integrated optical gyroscopes. Here, we analyze the effect of resonator losses on the rotational sensitivity of a coupled resonator optical waveguide (CROW) gyroscope in comparison to a single passive resonator gyroscope of the same size. We show that the CROW gyro offers a superior sensitivity only for very low propagation losses. Moreover, the single ring resonator gyro is found to have a sensitivity that is stable over wide range of resonator losses as well as boasting greater sensitivities than the CROW gyro for propagation losses in the resonators exceeding 10⁻¹  dB/cm.

Quantum inductance and high frequency oscillators in graphene nanoribbons

Here we investigate high frequency AC transport through narrow graphene nanoribbons with top-gate potentials that form a localized quantum dot. We show that as a consequence of the finite dwell time of an electron inside the quantum dot (QD), the QD behaves like a classical inductor at sufficiently high frequencies ω ≥ GHz. When the geometric capacitance of the top-gate and the quantum capacitance of the nanoribbon are accounted for, the admittance of the device behaves like a classical serial RLC circuit with resonant frequencies ω ∼ 100-900 GHz and Q-factors greater than 10(6). These results indicate that graphene nanoribbons can serve as all-electronic ultra-high frequency oscillators and filters, thereby extending the reach of high frequency electronics into new domains.

Bistable spin currents from quantum dots embedded in a microcavity

We examine the spin current generated by quantum dots embedded in an optical microcavity. The dots are connected to leads, which allow electrons to tunnel into and out of the dot. The spin current is generated by spin flip transitions induced by a quantized electromagnetic field inside the cavity with one of the Zeeman states lying below the Fermi level of the leads and the other above. In the limit of strong Coulomb blockade, this model is analogous to the Jaynes-Cummings model in quantum optics. We find that the cavity field amplitude and the spin current exhibit bistability as a function of the laser amplitude, which is driving the cavity mode. Even in the limit of a single dot, the spin current and the Q distribution of the cavity field have a bimodal structure.

Inhibiting Three-Body Recombination in Atomic Bose-Einstein Condensates

We discuss the possibility of inhibiting three-body recombination in atomic Bose-Einstein condensates via the application of resonant 2pi laser pulses. These pulses result in the periodic change in the phase of the molecular state by pi, which leads to destructive interference between the decay amplitudes following successive pulses. We show that the decay rate can be reduced by several orders of magnitude under realistic conditions.