arXiv subjects

David DeMille

Publications and source records attributed to David DeMille.

At least 37 records · Page 2Linked to original sources

arXiv2021

Polarization Enhanced Deep Optical Dipole Trapping of $Λ$-cooled Polar Molecules

We demonstrate loading of SrF molecules into an optical dipole trap (ODT) via in-trap $Λ$-cooling. We find that this cooling can be optimized by a proper choice of relative ODT and $Λ$ beam polarizations. In this optimized configuration, we observe molecules with temperatures as low as 14(1) $μ$K in traps with depths up to 570 $μ$K. With optimized parameters, we transfer $\!\sim\!5$% of molecules from our radio-frequency magneto-optical trap into the ODT, at a density of $\sim\!2\times 10^{9}$ cm$^{-3}$, a phase space density of $\sim\!2\times 10^{-7}$, and with a trap lifetime of $\!\sim\!1$ s.

physics.atom-ph↗

arXiv2021

Suppression of the optical crosstalk in a multi-channel silicon photomultiplier array

We propose and study a method of optical crosstalk suppression for silicon photomultipliers (SiPMs) using optical filters. We demonstrate that attaching absorptive visible bandpass filters to the SiPM can substantially reduce the optical crosstalk. Measurements suggest that the absorption of near infrared light is important to achieve this suppression. The proposed technique can be easily applied to suppress the optical crosstalk in SiPMs in cases where filtering near infrared light is compatible with the application.

physics.ins-det↗

arXiv2020

CeNTREX: A new search for time-reversal symmetry violation in the $^{205}$Tl nucleus

The Cold molecule Nuclear Time-Reversal EXperiment (CeNTREX) is a new effort aiming for a significant increase in sensitivity over the best present upper bounds on the strength of hadronic time reversal ($T$) violating fundamental interactions. The experimental signature will be shifts in nuclear magnetic resonance frequencies of $^{205}$Tl in electrically-polarized thallium fluoride (TlF) molecules. Here we describe the motivation for studying these $T$-violating interactions and for using TlF to do so. To achieve higher sensitivity than earlier searches for $T$-violation in TlF, CeNTREX uses a cryogenic molecular beam source, optical state preparation and detection, and modern methods of coherent quantum state manipulation. Details of the measurement scheme and the current state of the apparatus are presented, with quantitative measurements of the TlF beam. Finally, the estimated sensitivity and methods to control systematic errors are discussed.

physics.atom-ph↗

arXiv2020

Measurement of the molecular dipole moment and the hyperfine and $Λ$-doublet splittings of the $B^3Π_1$ state of thallium fluoride

We report high-precision measurements on the thallium fluoride $\tilde{J} = 1$ hyperfine manifold of the $B^3Π_1$ ($ν= 0$) state. This state is of special interest because it is central to an optical cycling scheme that is envisioned to play an important role in enhancing the sensitivity of the CeNTREX nuclear Schiff-moment experiment presently under construction. The measurements are made by monitoring the fluorescence induced by narrow-band laser excitation of a cryogenic molecular beam. We use a multipass arrangement of the laser beam to enhance fluorescence. When viewed with a camera, we can spatially resolve images from adjacent passes that approach the molecules from opposing directions. These images yield a sensitive visual method to identify the central frequency of a transition. Coupling these line-center determinations with frequency calibration from an acousto-optic modulator has allowed a more precise determination of the $\tilde{J} = 1$ manifold of hyperfine level splittings. We observe Stark shifts of the $\tilde{J} = 1$ levels and infer a permanent electric dipole moment of 2.28(7) D and $Λ$-doublet splittings for the $F_1' = 1/2$ and $F_1' = 3/2$ manifolds of 14.4(9) MHz and 17.4(11) MHz, respectively.

physics.atom-ph↗

arXiv2019

The metastable Q $^3Δ_2$ state of ThO: A new resource for the ACME electron EDM search

The best upper limit for the electron electric dipole moment was recently set by the ACME collaboration. This experiment measures an electron spin-precession in a cold beam of ThO molecules in their metastable $H~(^3Δ_1)$ state. Improvement in the statistical and systematic uncertainties is possible with more efficient use of molecules from the source and better magnetometry in the experiment, respectively. Here, we report measurements of several relevant properties of the long-lived $Q~(^3Δ_2)$ state of ThO, and show that this state is a very useful resource for both these purposes. The $Q$ state lifetime is long enough that its decay during the time of flight in the ACME beam experiment is negligible. The large electric dipole moment measured for the $Q$ state, giving rise to a large linear Stark shift, is ideal for an electrostatic lens that increases the fraction of molecules detected downstream. The measured magnetic moment of the $Q$ state is also large enough to be used as a sensitive co-magnetometer in ACME. Finally, we show that the $Q$ state has a large transition dipole moment to the $C~(^1Π_1)$ state, which allows for efficient population transfer between the ground state $X~(^1Σ^+)$ and the $Q$ state via $X-C-Q$ Stimulated Raman Adiabatic Passage (STIRAP). We demonstrate $90\,$% STIRAP transfer efficiency. In the course of these measurements, we also determine the magnetic moment of $C$ state, the $X\rightarrow C$ transition dipole moment, and branching ratios of decays from the $C$ state.

physics.atom-ph↗

arXiv2018

Injection-locking of a fiber-pigtailed laser to an external cavity diode laser via fiber optic circulator

We report a simple tunable master-slave laser injection-lock scheme for atomic physics experiments. Seed light from an external cavity diode laser is injected into a high-power fiber-pigtailed diode laser via a fiber optic circulator. High-power outputs (up to $\sim$600 mW) at the injected frequency have been obtained in a single-mode fiber with tuning over a wide wavelength range ($\sim$15 nm). The scheme is simpler and more cost-effective than the traditional scheme of free-space injection-locking.

physics.atom-ph↗

arXiv2018

Statistical sensitivity of phase measurements via laser-induced fluorescence with optical cycling detection

In atomic and molecular phase measurements using laser-induced fluorescence detection, optical cycling can enhance the effective photon detection efficiency and hence improve sensitivity. We show that detecting many photons per atom or molecule, while necessary, is not a sufficient condition to approach the quantum projection limit for detection of the phase in a two-level system. In particular, detecting the maximum number of photons from an imperfectly closed optical cycle reduces the signal-to-noise ratio (SNR) by a factor of $\sqrt{2}$, compared to the ideal case in which leakage from the optical cycle is sufficiently small. We derive a general result for the SNR in a system in terms of the photon detection efficiency, probability for leakage out of the optical cycle per scattered photon, and the product of the average photon scattering rate and total scattering time per atom or molecule.

physics.atom-ph↗

arXiv2018

Continuous Production of Rovibronic Ground State RbCs Molecules via Short-Range Photoassociation to the $b^3Π_{1}-c^3Σ^+_{1}-B^1Π_1$ States

We have investigated rovibronic levels of the strongly mixed $b^3Π_1-c^3Σ^+_1-B^1Π_1$ states [the 2(1), 3(1), and 4(1) states in Hund's case (c) notation] of $^{85}$Rb$^{133}$Cs in the energy range of 13950$-$14200 cm$^{-1}$ using short-range photoassociation (PA). For selected PA states, vibrational and rotational branching in the $X^1Σ^+$ state have been investigated using resonance-enhanced multiphoton ionization and depletion spectroscopy. Efficient production of $^{85}$Rb$^{133}$Cs molecules in the rovibronic ground state $X^1Σ^+ (v=0, J=0)$, at up to $\sim$1$\times 10^4$ molecules/s, has been achieved.

physics.atom-ph↗

arXiv2018

Measuring Nuclear Spin Dependent Parity Violation With Molecules: Experimental Methods and Analysis of Systematic Errors

Nuclear spin-dependent parity violation (NSD-PV) effects in atoms and molecules arise from $Z^0$ boson exchange between electrons and the nucleus, and from the magnetic interaction between electrons and the parity-violating nuclear anapole moment. It has been proposed to study NSD-PV effects using an enhancement of the observable effect in diatomic molecules [D. DeMille $\textit{et al.}$, Phys. Rev. Lett. $\textbf{100}$, 023003 (2008)]. Here, we demonstrate measurements of this type with sensitivity surpassing that of any previous atomic PV measurement, using the test system ${^{138}\mathrm{Ba^{19}F}}$. We show that systematic errors associated with our technique can be suppressed to at least the level of the present statistical sensitivity. With $\sim\!170$ hours of data, we measure the matrix element, $W$, of the NSD-PV interaction with uncertainty $δW/(2π)<0.7$ Hz, for each of two configurations where $W$ must have different signs. This sensitivity would be sufficient to measure NSD-PV effects of the size anticipated across a wide range of nuclei.

physics.atom-ph↗

arXiv2018

Demonstration of a Sensitive Method to Measure Nuclear Spin-Dependent Parity Violation

Nuclear spin-dependent parity violation (NSD-PV) effects in atoms and molecules arise from $Z^0$ boson exchange between electrons and the nucleus, and from the magnetic interaction between electrons and the parity-violating nuclear anapole moment. We demonstrate measurements of NSD-PV that use an enhancement of the effect in diatomic molecules, here using the test system $^{138}$Ba$^{19}$F. Our sensitivity surpasses that of any previous atomic PV measurement. We show that systematic errors can be suppressed to at least the level of the present statistical sensitivity. We measure the matrix element, $W$, of the NSD-PV interaction with total uncertainty $δW/(2π)<0.7$ Hz, for each of two configurations where $W$ must have different signs. This sensitivity would be sufficient to measure NSD-PV effects of the size anticipated across a wide range of nuclei.

physics.atom-ph↗

arXiv2017

Hyperfine Structure of the $B^3Π_1$ State and Predictions of Optical Cycling Behavior in the $X\rightarrow B$ transition of TlF

The rotational and hyperfine spectrum of the $X^1Σ^+ \rightarrow B^3Π_1$ transition in TlF molecules was measured using laser-induced fluorescence from both a thermal and a cryogenic molecular beam. Rotational and hyperfine constants for the $B$ state are obtained. The large magnetic hyperfine interaction of the Tl nuclear spin leads to significant mixing of the lowest $B$ state rotational levels. Updated, more precise measurements of the $B\rightarrow X$ vibrational branching fractions are also presented. The combined rovibrational branching fractions allow for the prediction of the number of photons that can be scattered in a given TlF optical cycling scheme.

physics.atom-ph↗

arXiv2016

Methods, Analysis, and the Treatment of Systematic Errors for the Electron Electric Dipole Moment Search in Thorium Monoxide

We recently set a new limit on the electric dipole moment of the electron (eEDM) (J. Baron et al., ACME collaboration, Science 343 (2014), 269-272), which represented an order-of-magnitude improvement on the previous limit and placed more stringent constraints on many CP-violating extensions to the Standard Model. In this paper we discuss the measurement in detail. The experimental method and associated apparatus are described, together with the techniques used to isolate the eEDM signal. In particular, we detail the way experimental switches were used to suppress effects that can mimic the signal of interest. The methods used to search for systematic errors, and models explaining observed systematic errors, are also described. We briefly discuss possible improvements to the experiment.

physics.atom-ph↗

arXiv2016

An Underappreciated Radiation Hazard from High Voltage Electrodes in Vacuum

The use of high voltage (HV) electrodes in vacuum is commonplace in physics laboratories. In such systems, it has long been known that electron emission from an HV cathode can lead to bremsstrahlung X-rays; indeed, this is the basic principle behind the operation of standard X-ray sources. However, in laboratory setups where X-ray production is not the goal and no electron source is deliberately introduced, field-emitted electrons accelerated by HV can produce X-rays as an unintended hazardous byproduct. Both the level of hazard and the safe operating regimes for HV vacuum electrode systems are not widely appreciated, at least in university laboratories. A reinforced awareness of the radiation hazards associated with vacuum HV setups would be beneficial. We present a case study of a HV vacuum electrode device operated in a university atomic physics laboratory. We describe the characterisation of the observed X-ray radiation, its relation to the observed leakage current in the device, the steps taken to contain and mitigate the radiation hazard, and suggest safety guidelines.

physics.med-ph↗

arXiv2016

In-vacuum scattered light reduction with cupric oxide surfaces for sensitive fluorescence detection

We demonstrate a simple and easy method for producing low-reflectivity surfaces that are ultra-high vacuum compatible, may be baked to high temperatures, and are easily applied even on complex surface geometries. Black cupric oxide (CuO) surfaces are chemically grown in minutes on any copper surface, allowing for low-cost, rapid prototyping and production. The reflective properties are measured to be comparable to commercially available products for creating optically black surfaces. We describe a vacuum apparatus which uses multiple blackened copper surfaces for sensitive, low-background detection of molecules using laser-induced fluorescence.

physics.ins-det↗

arXiv2014

Production of rovibronic ground state RbCs molecules via two-photon cascade decay

We report the production of ultracold RbCs molecules in the rovibronic ground state, i.e., $X^1Σ^+ (v=0, J=0)$, by short-range photoassociation to the $2^3Π_{0}$ state followed by spontaneous emission. We use narrowband depletion spectroscopy to probe the distribution of rotational levels formed in the $X ^1Σ^+(v=0)$ state. We conclude, based on selection rules, that the primary decay route to $X ^1Σ^+(v=0)$ is a two-step cascade decay that leads to as much as $33\%$ branching into the $J=0$ rotational level. The experimental simplicity of our scheme opens up the possibility of easier access to the study and manipulation of ultracold heteronuclear molecules in the rovibronic ground state.

physics.atom-ph↗

arXiv2013

Order of Magnitude Smaller Limit on the Electric Dipole Moment of the Electron

The Standard Model (SM) of particle physics fails to explain dark matter and why matter survived annihilation with antimatter following the Big Bang. Extensions to the SM, such as weak-scale Supersymmetry, may explain one or both of these phenomena by positing the existence of new particles and interactions that are asymmetric under time-reversal (T). These theories nearly always predict a small, yet potentially measurable ($10^{-27}$-$10^{-30}$ $e$ cm) electron electric dipole moment (EDM, $d_e$), which is an asymmetric charge distribution along the spin ($\vec{S}$). The EDM is also asymmetric under T. Using the polar molecule thorium monoxide (ThO), we measure $d_e = (-2.1 \pm 3.7_\mathrm{stat} \pm 2.5_\mathrm{syst})\times 10^{-29}$ $e$ cm. This corresponds to an upper limit of $|d_e| < 8.7\times 10^{-29}$ $e$ cm with 90 percent confidence, an order of magnitude improvement in sensitivity compared to the previous best limits. Our result constrains T-violating physics at the TeV energy scale.

physics.atom-ph↗

arXiv2013

Advanced Cold Molecule Electron EDM

Measurement of a non-zero electric dipole moment (EDM) of the electron within a few orders of magnitude of the current best limit of |d_e| < 1.05 e -27 e cm would be an indication of physics beyond the Standard Model. The ACME Collaboration is searching for an electron EDM by performing a precision measurement of electron spin precession in the metastable H state of thorium monoxide (ThO) using a slow, cryogenic beam. We discuss the current status of the experiment. Based on a data set acquired from 14 hours of running time over a period of 2 days, we have achieved a 1-sigma statistical uncertainty of 1 e -28 e cm/T^(1/2), where T is the running time in days.

physics.atom-ph↗

arXiv2011

Magnetic and electric dipole moments of the $H\ {}^3Δ_1$ state in ThO

The metastable $H \ {}^3Δ_1$ state in the thorium monoxide (ThO) molecule is highly sensitive to the presence of a CP-violating permanent electric dipole moment of the electron (eEDM). The magnetic dipole moment $μ_H$ and the molecule-fixed electric dipole moment $D_H$ of this state are measured in preparation for a search for the eEDM. The small magnetic moment $μ_H = 8.5(5) \times 10^{-3} \ μ_B$ displays the predicted cancellation of spin and orbital contributions in a ${}^3 Δ_1$ paramagnetic molecular state, providing a significant advantage for the suppression of magnetic field noise and related systematic effects in the eEDM search. In addition, the induced electric dipole moment is shown to be fully saturated in very modest electric fields ($<$ 10 V/cm). This feature is favorable for the suppression of many other potential systematic errors in the ThO eEDM search experiment.

physics.atom-ph↗