arXiv subjects

M R Tarbutt

Publications and source records attributed to M R Tarbutt.

5 recordsLinked to original sources

arXiv2023

Demonstration and frequency noise characterization of a 17 $\mu$m quantum cascade laser

We evaluate the spectral performance of a novel continuous-wave room-temperature distributed feedback quantum cascade laser operating at the long wavelength of 17 $\mu$m. By demonstrating broadband laser absorption spectroscopy of the $\nu$2 fundamental vibrational mode of N2O molecules, we have determined the spectral range and established the spectroscopic potential of this laser. We have characterized the frequency noise and measured the line width of this new device, uncovering a discrepancy with the current consensus on the theoretical modeling of quantum cascade lasers. Our results confirm the potential of such novel narrow-line-width sources for vibrational spectroscopy. Extending laser spectroscopy to longer wavelength is a fascinating prospect that paves the way for a wide range of opportunities from chemical detection, to frequency metrology as well as for exploring light-matter interaction with an extended variety of molecules, from ultra-cold diatomic species to increasingly complex molecular systems.

physics.atom-ph↗

arXiv2019

Ultracold polar molecules as qudits

We discuss how the internal structure of ultracold molecules, trapped in the motional ground state of optical tweezers, can be used to implement qudits. We explore the rotational, fine and hyperfine structure of $^{40}$Ca$^{19}$F and $^{87}$Rb$^{133}$Cs, which are examples of molecules with $^2Σ$ and $^1Σ$ electronic ground states, respectively. In each case we identify a subset of levels within a single rotational manifold suitable to implement a 4-level qudit. Quantum gates can be implemented using two-photon microwave transitions via levels in a neighboring rotational manifold. We discuss limitations to the usefulness of molecular qudits, arising from off-resonant excitation and decoherence. As an example, we present a protocol for using a molecular qudit of dimension $d=4$ to perform the Deutsch algorithm.

quant-ph↗

arXiv2018

Ultracold molecules for quantum simulation: rotational coherences in CaF and RbCs

We explore the uses of ultracold molecules as a platform for future experiments in the field of quantum simulation, focusing on two molecular species, $^{40}$Ca$^{19}$F and $^{87}$Rb$^{133}$Cs. We report the development of coherent quantum state control using microwave fields in both molecular species; this is a crucial ingredient for many quantum simulation applications. We demonstrate proof-of-principle Ramsey interferometry measurements with fringe spacings of $\sim 1~\rm kHz$ and investigate the dephasing time of a superposition of $N=0$ and $N=1$ rotational states when the molecules are confined. For both molecules, we show that a judicious choice of molecular hyperfine states minimises the impact of spatially varying transition-frequency shifts across the trap. For magnetically trapped $^{40}$Ca$^{19}$F we use a magnetically insensitive transition and observe a coherence time of 0.61(3) ms. For optically trapped $^{87}$Rb$^{133}$Cs we exploit an avoided crossing in the AC Stark shift and observe a maximum coherence time of 0.75(6) ms.

cond-mat.quant-gas↗

arXiv2016

Direct loading of a large Yb MOT on the $^{1}S_{0} \rightarrow \, ^{3}P_{1}$ transition

We report a robust technique for laser frequency stabilisation that enables the reproducible loading of in excess of 10$^{9}$ Yb atoms from a Zeeman slower directly into a magneto-optical trap (MOT) operating on the $^{1}S_{0} \rightarrow \, ^{3}P_{1}$ transition, without the need for a first stage MOT on the $^{1}S_{0} \rightarrow \, ^{1}P_{1}$ transition. We use a simple atomic beam apparatus to generate narrow fluorescence signals on both the 399 nm $^{1}S_{0} \rightarrow \, ^{1}P_{1}$ transition used for the Zeeman slower and the 556 nm $^{1}S_{0} \rightarrow \, ^{3}P_{1}$ transition. We present in detail the methods for obtaining spectra with a high signal-to-noise ratio and demonstrate error signals suitable for robust frequency stabilisation. Finally we demonstrate the stability and precision of our technique through sensitive measurements of the gravitational sag of the Yb MOT as a function of the intensity of the laser cooling beams, which are in good agreement with theory. These results will be important for efficient loading of the atoms into an optical dipole trap.

physics.atom-ph↗

arXiv2013

Stochastic multi-channel lock-in detection

High-precision measurements benefit from lock-in detection of small signals. Here we discuss the extension of lock-in detection to many channels, using mutually orthogonal modulation waveforms, and show how the the choice of waveforms affects the information content of the signal. We also consider how well the detection scheme rejects noise, both random and correlated. We address the particular difficulty of rejecting a background drift that makes a reproducible offset in the output signal and we show how a systematic error can be avoided by changing the waveforms between runs and averaging over many runs. These advances made possible a recent measurement of the electron's electric dipole moment.

physics.ins-det↗