D. W. Vernooy

High-Q measurements of fused-silica microspheres in the near infrared

Measurements of the quality factor Q approximately 8x10(9) are reported for the whispering-gallery modes (WGMs) of quartz microspheres for the wavelengths 670, 780, and 850 nm; these results correspond to finesse f approximately 2.2x10(6) . The observed independence of Q from wavelength indicates that losses for the WGMs are dominated by a mechanism other than bulk absorption in fused silica in the near infrared. Data obtained by atomic force microscopy combined with a simple model for surface scattering suggest that Q can be limited by residual surface inhomogeneities. Absorption by absorbed water can also explain why the material limit is not reached at longer wavelengths in the near infrared.

Trapping of Single Atoms in Cavity QED

By integrating the techniques of laser cooling and trapping with those of cavity quantum electrodynamics (QED), single cesium atoms have been trapped within the mode of a small, high finesse optical cavity in a regime of strong coupling. The observed lifetime for individual atoms trapped within the cavity mode is τ≈28 ms, and is limited by fluctuations of light forces arising from the far-detuned intracavity field. This initial realization of trapped atoms in cavity QED should enable diverse protocols in quantum information science.

High performance planar lightwave circuit triplexer with passive optical assembly

High performance, compact planar lightwave circuit based triplexers have been built and tested. The triplexers utilize lasers, photodiodes and filters that have been adapted to enable passive optical assembly of the triplexer.

Quantum manipulation and measurement of single atoms in optical cavity QED

Summary form only given. Using cold atoms strongly interacting with individual photons inside a high finesse cavity, we are approaching an ideal quantum system in which both matter (internal and external degrees of freedom) and light exhibit strong quantum character and the systems coherent evolution dominates decoherence processes. With this system we have performed real-time continuous measurement of single atomic spatial trajectories. The measurement protocol involves the determination of the phase of the cavity output field, which is far-detuned from the atomic resonance to minimize the measurement back action on the center-of-mass (CM) motion. The real-time evolution of the complex field amplitude is efficiently recorded at high bandwidth and with good signal-to-noise ratio, limited respectively by the rate of coherent coupling between atom and cavity mode and the photodetection shot noise. This nearly optimal detection technique has already revealed atomic CM motion inside the cavity standing-wave field of single photons, and should eventually lead to the strong conditioning of system evolution on measurement results and the realization of quantum feedback control. Another related but independent experiment concentrates on quantum manipulation of the CM motion. Owing to the highest coherent coupling rate between cavity field and individual atoms achieved to date, the mechanical coupling between atom and cavity can be significantly larger than the kinetic energy of laser cooled atoms, even under very low cavity excitation. Indeed, evidence of mechanical light forces for intracavity photon number <1 has already been observed. The origin of this mechanical force is radically different from that in conventional laser trapping where photon scattering (coherent or incoherent) drives the atomic CM motion. The spatial variation of the standing cavity mode (and hence of the atom-field coupling), produce optical potentials capable of localizing atoms inside the cavity. With the initial evidence of prolonged atomic transit through the cavity field (by 3/spl times/) when the suitable trapping state (the lower dressed state of the atom-cavity system) was excited, we are working towards suppression of the atomic momentum diffusion to achieve long-term atomic confinement via quantum feedback.

Surface mount photonics as a platform for optoelectronic packaging

A planar lightwave circuit (PLC) based optoelectronic packaging platform is described. Features include completely passive, performance-insensitive alignment for all devices to +/- 2 microns, glob-top encapsulation to eliminate hermetic packaging and wafer-level test and burn-in.

Real-time tracking and trapping of single atoms in cavity QED

Cavity quantum electrodynamics (QED) offers powerful possibilities for the deterministic control of atom-photon interactions quantum by quantum [1]. Indeed, modern experiments in cavity QED have achieved the exceptional circumstance of strong coupling, for which single quanta can profoundly impact the dynamics of the atom-cavity system. The diverse accomplishments of this field set the stage for advances into yet broader frontiers in quantum information science for which cavity QED offers unique advantages, such as the realization of quantum networks by way of multiple atom-cavity systems linked by optical interconnects [2,3].

Cavity Quantum Electrodynamics with a Capital Q

With recent developments in optical cavity QED pioneered in the Quantum Optics Group at Caltech, optical physics has progressed to a domain wherein processes are driven by single atoms interacting with optical fields with average energy corresponding to much less than one photon. This unique situation opens doors for new and exciting phenomena which manifestly rely on the quantum nature of the atom-field interaction. The system that we have developed to access this realm consists of an atom strongly coupled to a single mode of a high finesse optical resonator [1]. To introduce the notation, the dipole coupling of the atom to the cavity mode is described by a rate g, while the dissipative rates are γ || for atomic energy decay (with the polarization decay rate γ ┴ = γ || /2 as appropriate for purely radiative relaxation) and k for cavity decay.

Quantum communication and computation in quantum optics

Summary form only given. In the quantum optics group at Caltech, we are attempting to lay the foundations for quantum information science by way of advances on several fronts in optical physics. Within the setting of cavity QED, single atoms are strongly coupled to the field of a high finesse optical cavity at the single photon level, with current work directed toward trapping and localization of atoms inside the cavity. Although there are daunting technical problems to overcome, a principal scientific objective is the creation of quantum networks to implement fundamental quantum communication protocols and for distributed quantum computation. Beyond quantum information processing with internal atomic states and photons serving as qubits, we are also investigating algorithms for continuous quantum variables. A recent example is our realization of quantum teleportation for the quadrature amplitudes of a beam of light. The experiment utilizes squeezed-state entanglement to achieve unconditional quantum teleportation.

Measurement and control of single atom motions in the quantum regime

Using cold atoms strongly coupled to a high finesse optical cavity, we have performed real-time continuous measurement of single atomic trajectories in terms of the interaction energy (Eint) with the cavity. Individual transit events reveal a shot-noise limited measurement (fractional) sensitivity of 4×10−4/Hz to variations in Eint/ℏ within a bandwidth of 1–300 kHz. The strong coupling of atom and cavity leads to a maximum interaction energy greater than the kinetic energy of an intracavity laser-cooled atom, even under weak cavity excitation. Evidence of mechanical light forces for intracavity photon number <1 has been observed. The quantum character of the nonlinear optical response of the atom-cavity system is manifested for the trajectory of a single atom.

Cavity QED with Whispering Gallery Modes of Fused Silica Microspheres

The Whispering Gallery Modes of fused silica microspheres hold the promise for simultaneous achievement of high Q (> 109) and small mode volumes (<EQ 10-14 m3) necessary for strong coupling in cavity QED. Here we present results for high Q measurements into the NIR along with some progress towards experimental implementation in cavity QED.