arXiv subjects

Bryan Hemingway

Publications and source records attributed to Bryan Hemingway.

8 recordsLinked to original sources

arXiv2024

Cold Beam Optical Clock with Multifrequency Spectroscopy

We demonstrate an optical clock based on Ramsey-Bord\'e interferometry in a laser-cooled ${}^{40}$Ca beam. The mean velocity is reduced by an order of magnitude relative to a thermal beam and the transverse temperature approaches the Doppler limit, enabling the measurement of sub-kHz linewidth fringes in a compact interferometer. Using tailored phase and intensity modulation of the spectroscopy laser to add uniform frequency sidebands, we interrogate atoms throughout the transverse velocity distribution, increasing the Ramsey-Bord\'e fringe amplitude by a factor of 14 and improving the Allan deviation to $3.4\times 10^{-15}$ at one second averaging time.

physics.atom-ph↗

arXiv2022

Tellurium Spectrometer for ${}^1\text{S}_0-{}^{1}\text{P}_1$ Transitions in Strontium and Other Alkaline-Earth Atoms

We measure the spectrum of tellurium-130 in the vicinity of the 461~nm ${}^1\text{S}_0-{}^{1}\text{P}_1$ cycling transition in neutral strontium, a popular element for atomic clocks, quantum information, and quantum-degenerate gases. The lack of hyperfine structure in tellurium results in a spectral density of transitions nearly 50 times lower than that available in iodine, making use of tellurium as a laser-frequency reference challenging. By frequency-offset locking two lasers, we generate the large frequency shifts required to span the difference between a tellurium line and the ${}^1\text{S}_0-{}^1\text{P}_1$ resonance in strontium or other alkaline-earth atom. The resulting laser architecture is long-term frequency stable, widely tunable, and optimizes available laser power. The versatility of the system is demonstrated by using it to quickly switch between any strontium isotope in a magneto-optical trap and by adapting it to spectroscopy on a thermal beam with a different alkaline-earth atom.

physics.atom-ph↗

arXiv2020

Competition between Factors Determining Bright versus Dark Atomic States within a Laser Mode

We observe bimodal fluorescence patterns from atoms in a fast atomic beam when the laser excitation occurs in the presence of a magnetic field and the atoms sample only a portion of the laser profile. The behavior is well explained by competition between the local intensity of the laser, which tends to generate a coherent-population-trapping (CPT) dark state in the $J=1$ to $J'=0$ system, and the strength of an applied magnetic field that can frustrate the CPT process. This work is relevant for understanding and optimizing the detection process for clocks or other coherent systems utilizing these transitions and could be applicable to in situ calibration of the laser-atom interaction, such as the strength of the magnetic field or laser intensity at a specific location.

physics.atom-ph↗

arXiv2018

Vapor-cell frequency reference for short-wavelength transitions in neutral calcium

We have characterized the molecular tellurium (Te$_2$) spectrum in the vicinity of the 423nm $^1S_0-^1P_1$ and the 431nm $^3P_1-^3P_0$ transitions in neutral calcium. These transitions are relevant to optical clocks for atomic-beam characterization and cooling (423nm) and enhanced detection (431nm). The use of a Te$_2$ vapor cell as a frequency reference has many advantages over other laser stabilization techniques, and we discuss an application to measuring the instability due to the second-order Doppler shift in a calcium beam clock.

physics.atom-ph↗

arXiv2013

Dynamic response of a spin-1/2 Kondo singlet

We present a study of spin 1/2 Kondo singlets in single electron transistors under a microwave frequency bias excitation. We compare time-averaged conductance $G$ to predicted universal response with respect to microwave frequency, oscillation amplitude and the Kondo temperature and find a non-adiabatic response when the microwave photon energy $hf$ is comparable to the Kondo temperature $k_B T_K$. We show that our measurements are qualitatively consistent with the predictions for the radiation-induced decoherence rate of the Kondo spin.

cond-mat.str-el↗

arXiv2011

A quantitative study of spin-flip co-tunneling transport in a quantum dot

We report detailed transport measurements in a quantum dot in a spin-flip co-tunneling regime, and a quantitative comparison of the data to microscopic theory. The quantum dot is fabricated by lateral gating of a GaAs/AlGaAs heterostructure, and the conductance is measured in the presence of an in-plane Zeeman field. We focus on the ratio of the nonlinear conductance values at bias voltages exceeding the Zeeman threshold, a regime that permits a spin flip on the dot, to those below the Zeeman threshold, when the spin flip on the dot is energetically forbidden. The data obtained in three different odd-occupation dot states show good quantitative agreement with the theory with no adjustable parameters. We also compare the theoretical results to the predictions of a phenomenological form used previously for the analysis of non-linear co-tunneling conductance, specifically the determination of the heterostructure g-factor, and find good agreement between the two.

cond-mat.mes-hall↗

arXiv2009

Magnetic-Field-Induced Crossover to a Nonuniversal Regime in a Kondo Dot

We have measured the magnetic splitting, $Δ_K$, of a Kondo peak in the differential conductance of a Single-Electron Transistor while tuning the Kondo temperature, $T_K$, along two different paths in the parameter space: varying the dot-lead coupling at a constant dot energy, and vice versa. At a high magnetic field, $B$, the changes of $Δ_K$ with $T_K$ along the two paths have opposite signs, indicating that $Δ_K$ is not a universal function of $T_K$. At low $B$, we observe a decrease in $Δ_K$ with $T_K$ along both paths, in agreement with theoretical predictions. Furthermore, we find $Δ_K/Δ<1$ at low $B$ and $Δ_K/Δ>1$ at high $B$, where $Δ$ is the Zeeman energy of the bare spin, in the same system.

cond-mat.mes-hall↗

arXiv2009

Magnetic Splitting of the Zero Bias Peak in a Quantum Point Contact with a Variable Aspect Ratio

We report a zero-bias peak in the differential conductance of a Quantum Point Contact (QPC), which splits in an external magnetic field. The peak is observed over a range of device conductance values starting significantly below $2e^2/h$. The observed splitting closely matches the Zeeman energy and shows very little dependence on gate voltage, suggesting that the mechanism responsible for the formation of the peak involves electron spin. Precision Zeeman energy data for the experiment are obtained from a separately patterned single-electron transistor located a short distance away from the QPC. The QPC device has four gates arranged in a way that permits tuning of the longitudinal potential, and is fabricated in a GaAs/AlGaAs heterostructure containing 2-dimenional electron gas. We show that the agreement between the peak splitting and the Zeeman energy is robust with respect to moderate distortions of the QPC potential. We also show that the mechanism that leads to the formation of the ZBP is different from the conventional Kondo effect found in quantum dots.

cond-mat.mes-hall↗