Session T07: FOCUS: Ultrasensitive Atomic Sensors

Live

Optical trapping and the systems created by optically trapped particles have applications ranging from manipulations of single cells to precision force sensing and searches for new physics. In this work, the authors demonstrate a novel metrological application wherein an optically trapped and rotating microsphere is used as a spinning-rotor vacuum gauge. Rotation is induced electrostatically, by applying torque to the permanent electric dipole moment found in some silica microspheres, and measured optically, by analyzing the light transmitted through the microsphere. The kinetic theory of gases relates the torsional drag on a spinning microsphere to the pressure of residual gas in the immediate vicinity of the microsphere, calibrated by measuring the rotor mass with electrostatic co-levitation, and assuming a spherical shape and uniform density. Two distinct techniques allow the measurement of torsional drag in both moderate and high vacuum conditions. At moderate vacuum, torsional drag is measured as a phase lag between the electrostatic driving field and the rotation of the microsphere. At high vacuum, the time constant of exponential decay when the microsphere is released from a driving field is also related directly to the torsional drag.   

Live

We have shown that Rydberg atoms can be used for high-sensitivity, absolute sensing of high frequency electric fields. We have achieved high sensitivity using several different read-out strategies. These methods demonstrated read-out laser shot-noise limited performance. Fundamental limits to the sensitivity of the Rydberg atom-based RF electric field sensing have been addressed. Depending on the spectral resolution of the read-out, either the RF induced transmission line frequency splitting, the Autler-Townes regime, or a change in the on-resonant absorption, the amplitude regime, can be used to determine the RF electric field. In this paper we address some practical improvements to these methods. We present theoretical results of a 3-photon read-out scheme which enables the Autler-Townes regime of Rydberg atom-based RF electrometry to be extended to lower RF electric field strengths. We show experimentally that the residual Doppler shifts can be reduced and signal strengths increased using the approach. We also address implementing this strategy using small subwavelength vapor cells that we have constructed, which have extremely low scattering cross-sections and uniform fields in the measurement region. Imaging of electromagnetic fields at high data rates with the capacity to implement signal processing protocols not available using standard cameras will be described.   

Live

Defects in solids have emerged as a promising platform for quantum sensing. Leading candidates, such as nitrogen-vacancy color center in diamond, can be initialized into pure quantum states, can be coherently controlled, and can have relatively long-lived quantum coherence at room temperature. Lack of high-fidelity state readout, however, has limited the utility of solid-state quantum devices. Despite extensive experimental effort, no universal, readout technique has been achieved for solid-state spin ensembles. Here we demonstrate a novel, non-optical technique for readout using microwave-accessible transitions. By coupling ensembles of spins to a microwave cavity, we realize a dramatic enhancement of the state-dependent dispersive shift produced by the ensemble, paving the way for high-fidelity readout at room temperature. We demonstrate this technique by employing an ensemble of nitrogen vacancy centers for magnetometry, achieving a sensitivity unconstrained by optical photon shot noise.   

Live

At the National Institute of Standards and Technology we are building a Cold Atom Vacuum Standard (CAVS) device that will operate as a primary standard for the Ultra-High-Vacuum and Extreme-High-Vacuum regimes. Current pressure sensors do not operate reliably at these pressures. The CAVS device operates by relating loss of microkelvin lithium atoms from a shallow conservative trap by collisions with ambient, room-temperature atoms and molecules to the background density and thus pressure through the ideal gas law. The predominant background constituent at ultra low pressures is molecular hydrogen. After giving an introduction into pressure sensing technologies, I will describe our theoretical characterization of the lithium with hydrogen-dimer collision processes as well as that with atom helium, often injected to detect leaks in vacuum systems. Specifically, we computed the relevant Born-Oppenheimer potential energy surfaces, paying special attention to their uncertainty. Coupled-channels calculations were then used to obtain total rate coefficients, which include momentum-changing elastic and inelastic processes, with a 2\% relative uncertainty. We also showed that inelastic rotational quenching of the hydrogen dimer is negligible near room temperature.   

On Demand

We demonstrate the applicability of a new kind of gas sensor based on Rydberg excitations. From a gas mixture the molecule in question is excited to a Rydberg state. By succeeding collisions with all other gas components this molecule becomes ionized and the emerging electron can be measured as a current, which is the clear signature of the presence of this particular molecule. As a first test we excite Alkali Rydberg atoms in an electrically contacted vapor cell [1,2] and demonstrate a detection limit of 100\,ppb to a background of N$_2$. We employ our gas sensing scheme to the detection of nitric oxide at thermal temperatures and atmospheric pressure [3]. We show first results of cw spectroscopy of the A$\,{}^2\Sigma^+\leftarrow\,$X$\,{}^2\Pi_{1/2}$ transition in nitric oxide. [1] D. Barredo, et al., \textit{Phys. Rev. Lett.} \textbf{110}, 123002 (2013) [2] J. Schmidt, et al., SPIE \textbf{10674} (2018) [3] J. Schmidt, et al., \textit{Appl. Phys. Lett.} \textbf{113}, 011113 (2018)   

On Demand

In the quest for a sensor that can measure electric fields of arbitrary frequency, all potential platforms exhibit trade-offs between sensitivity, operational frequency range, and instantaneous bandwidth. Thermal vapors of Rydberg atoms, which are sensitive to fields ranging from DC to $\sim1$ THz, are a recent contender in this endeavor. We have previously shown quantum-limited performance in this system and characterized the instantaneous bandwidth; however, a quantitative measure of the sensitivity, particularly in relation to other mature sensor technologies, has not been performed. Here I will present such an assessment, derived from first principles, of the sensitivity to fields spanning 1 kHz to 1 THz and I will compare this to the performance of ideal dipole antenna-couple passive electronics and electro-optic crystals. I will highlight current limitations and potential areas of significant improvement for the Rydberg sensor.   

Ultrahigh-sensitive sensor based on giant Lamb shift in a strongly coupled plasmonic-emitter system

Lamb shift is one of the most important quantum effects in quantum electrodynamics (QED). However, it is usually very small in the normal vacuum and is hard to be detected. Here, we show that due to the tightly confined vacuum field the photonic Lamb shift of a quantum emitter near a plasmonic nanostructure can be huge. Instead of measuring the emission of the quantum emitter itself, we show that the amplified Lamb shift of the emitter can also be observed from the absorption spectrum of the plasmonic structure which couples to the quantum emitter. Furthermore, we show for the first time that the Lamb shift can be used to preciously measure the emitter position and dipole orientation which may find important applications as a high sensitive sensor.