Photonic integrated beam delivery for a rubidium 3D magneto-optical trap.

Cold atoms are important for precision atomic applications including timekeeping and sensing. The 3D magneto-optical trap (3D-MOT), used to produce cold atoms, will benefit from photonic integration to improve reliability and reduce size, weight, and cost. These traps require the delivery of multiple, large area, collimated laser beams to an atomic vacuum cell. Yet, to date, beam delivery using an integrated waveguide approach has remained elusive. Here we report the demonstration of a 87Rb 3D-MOT using a fiber-coupled photonic integrated circuit to deliver all beams to cool and trap > 1 ×106 atoms to near 200 µK. The silicon nitride photonic circuit transforms fiber-coupled 780 nm cooling and repump light via waveguides to three mm-width non-diverging free-space cooling and repump beams directly to the rubidium cell. This planar, CMOS foundry-compatible integrated beam delivery is compatible with other components, such as lasers and modulators, promising system-on-chip solutions for cold atom applications.

Intra-cavity frequency-doubled VECSEL system for narrow linewidth Rydberg EIT spectroscopy.

High-power, narrow-linewidth light sources in the visible and UV spectra are in growing demand, particularly as quantum information and sensing research proliferates. Vertical external-cavity surface-emitting lasers (VECSELs) with intra-cavity frequency conversion are emerging as an attractive platform to fill these needs. Using such a device, we demonstrate 3.5 MHz full-width half-maximum Rydberg-state spectroscopy via electromagnetically induced transparency (EIT). The laser's 690 mW of output power at a wavelength of 475 nm enables large Rabi frequencies and strong signal-to-noise ratio in shorter measurement times. In addition, we characterize the frequency stability of the VECSEL using the delayed self-heterodyne technique and direct comparison with a commercial external-cavity diode laser (ECDL). We measure the pre-doubled light's Lorentzian linewidth to be 2π × 5.3(2) kHz, and the total linewidth to be 2π × 23(2) kHz. These measurements provide evidence that intra-cavity frequency-doubled VECSELs can perform precision spectroscopy at and below the MHz level, and are a promising tool for contemporary, and future, quantum technologies.

Spin-Wave Multiplexed Atom-Cavity Electrodynamics.

We introduce multiplexed atom-cavity quantum electrodynamics with an atomic ensemble coupled to a single optical cavity mode. Multiple Raman dressing beams establish cavity-coupled spin-wave excitations with distinctive spatial profiles. Experimentally, we demonstrate the concept by observing spin-wave vacuum Rabi splittings, selective superradiance, and interference in the cavity-mediated interactions of two spin waves. We highlight that the current experimental configuration allows rapid, interchangeable cavity coupling to 4 profiles with an overlap parameter of less than 10%, enough to demonstrate, for example, a quantum repeater network simulation in the cavity. With further improvements to the optical multiplexing setup, we infer the ability to access more than 10^{3} independent spin-wave profiles.

Quantum-Limited Atomic Receiver in the Electrically Small Regime.

We use a quantum sensor based on thermal Rydberg atoms to receive data encoded in electromagnetic fields in the extreme electrically small regime, with a sensing volume over 10^{7} times smaller than the cube of the electric field wavelength. We introduce the standard quantum limit for data capacity, and experimentally observe quantum-limited data reception for bandwidths from 10 kHz up to 30 MHz. In doing this, we provide a useful alternative to classical communication antennas, which become increasingly ineffective when the size of the antenna is significantly smaller than the wavelength of the electromagnetic field.

Twists in nonlinear magneto-optic rotation with cold atoms.

We observe a narrow secondary dispersive feature nested within conventional nonlinear magneto-optical rotation (NMOR) signals obtained with a laser-cooled rubidium vapor. A similar feature has been previously named a "twist" by Budker et. al., in the context of warm vapor optical magnetometry [Phys. Rev. A. 81, 5788-5791 (1998)], and was ascribed to simultaneous optical pumping through multiple nearby hyperfine levels. In this work the twist is observed in a cold atom vapor, where the hyperfine levels are individually addressable, and thus is due to a different mechanism. We experimentally and numerically characterize this twist in terms of magnetic field strength, polarization, and optical intensity and find good agreement between our data and numerical models. We find that the twist width is proportional to the magnetic field in the transverse direction, and therefore two independent directions of the magnetic field can be measured simultaneously. This technique is useful as a simple and rapid in-situ method for nulling background magnetic fields.

Nonlinear polarization spectroscopy of a Rydberg state for laser stabilization.

We demonstrate modulation-free laser stabilization to an atomic Rydberg transition using nonlinear polarization spectroscopy. To stabilize a laser to the upper transition of a three-level ladder scheme, the techniques of standard polarization spectroscopy are adapted to use a narrow, nonlinear coherence feature. We obtain a subnatural linewidth dispersive signal that is directly suitable for laser frequency stabilization. We examine the effect of laser polarization on the dispersive line shape. This technique stabilizes the laser to an absolute frequency reference, can be used with numerous Rydberg levels, and eliminates laser modulation, which can enable high bandwidth feedback.

Polarization-enhanced absorption spectroscopy for laser stabilization.

We demonstrate a variation of pump-probe spectroscopy that is particularly useful for laser frequency stabilization. The polarization-enhanced absorption spectroscopy (POLEAS) signal provides a significant improvement in signal-to-noise ratio over saturated absorption spectroscopy (SAS) for the important and commonly used atomic cycling transitions. The improvements can directly increase the short-term stability of a laser frequency lock, given sufficient servo loop bandwidth. The long-term stability of the POLEAS method, which is limited by environmental sensitivities, is comparable to that of SAS. The POLEAS signal is automatically Doppler-free, without requiring a separate Doppler subtraction beam, and lends itself to straightforward compact packaging. Finally, by increasing the amplitude of the desired (cycling) peak, while reducing the amplitude of all other peaks in the manifold, the POLEAS method eases the implementation of laser auto-locking schemes.