arXiv subjects

S. D. Hogan

Publications and source records attributed to S. D. Hogan.

At least 19 recordsLinked to original sources

arXiv2025

Determining Absolute Neutrino Mass using Quantum Technologies

Next generation tritium decay experiments to determine the absolute neutrino mass require high-precision measurements of $β$-decay electron energies close to the kinematic end point. To achieve this, the development of high phase-space density sources of atomic tritium is required, along with the implementation of methods to control the motion of these atoms to allow extended observation times. A promising approach to efficiently and accurately measure the kinetic energies of individual $β$-decay electrons generated in these dilute atomic gases, is to determine the frequency of the cyclotron radiation they emit in a precisely characterised magnetic field. This cyclotron radiation emission spectroscopy technique can benefit from recent developments in quantum technologies. Absolute static-field magnetometry and electrometry, which is essential for the precise determination of the electron kinetic energies from the frequency of their emitted cyclotron radiation, can be performed using atoms in superpositions of circular Rydberg states. Quantum-limited microwave amplifiers will allow precise cyclotron frequency measurements to be made with maximal signal-to-noise ratios and minimal observation times. Exploiting the opportunities offered by quantum technologies in these key areas, represents the core activity of the Quantum Technologies for Neutrino Mass project. Its goal is to develop a new experimental apparatus that can enable a determination of the absolute neutrino mass with a sensitivity on the order of 10~meV/$c^2$.

hep-ex↗

arXiv2025

Observation of resonant monopole-dipole energy transfer between Rydberg atoms and polar molecules

Resonant energy transfer (RET), between equal parity 1s65s$^3\mathrm{S}_1$ and 1s66s$^3\mathrm{S}_1$ Rydberg levels in helium has been observed in low-temperature ($\sim80$ mK) collisions with ammonia molecules which undergo inversion transitions in their X$^1$A$_1$ ground electronic state. This hybrid Rydberg-atom-polar-molecule RET represents a monopole-dipole energy exchange reaction that necessarily requires spatial overlap of the Rydberg-electron and molecular wavefunctions. Calculations, that account explicitly for the charge-dipole interaction between the Rydberg electron and the molecule, provide a quantitative explanation of the observations. Total parity is conserved in the reaction through the mixing of collisional angular momentum in the atom-molecule complex. This work opens opportunities to expand the toolbox for quantum science with charge-dipole-mediated energy exchange in hybrid neutral-atom-polar-molecule platforms.

physics.atom-ph↗

arXiv2025

Interfacing Rydberg atoms with a chip-based superconducting microwave resonator using an ac-Stark-shifted single-photon transition

Helium atoms in the 1s50s$\,^3$S$_1$ Rydberg level have been resonantly coupled to the $2\pi\times11.722$ GHz second harmonic mode of a chip-based superconducting coplanar waveguide microwave resonator. To achieve this, the single-photon electric-dipole-allowed 1s50s$\,^3$S$_1\rightarrow$ 1s50p$\,^3$P$_J$ transition was tuned into resonance with the resonator mode through the AC Stark shift induced by a second strong $2\pi\times3.350$ GHz microwave dressing field. The effects of this dressing field, and residual uncanceled DC electric fields at the location of the atoms close to the superconducting chip surface were interpreted with support from Floquet calculations of the energy level structure of the Rydberg states. To observe appreciable population transfer in the $1~\mu$s atom-resonator interaction time using this transition, which had an electric dipole moment of $1500\,e\,a_0$, pulsed microwave fields were injected into the resonator. From the photon occupation number in the resonator mode under these conditions, the single-photon Rabi frequency associated with the coupling of the atoms to the resonator was estimated to be $\sim2\pi\times100$ Hz. These results represent an important step toward operation of this Rydberg-atom-superconducting-circuit interface in the single-photon strong coupling regime.

physics.atom-ph↗

arXiv2024

Electrostatic trapping of N$_2$ molecules in high Rydberg states

N$_2$ molecules traveling in pulsed supersonic beams have been excited from their ${\mathrm{X\,^1Σ_{\mathrm{g}}^+}}$ ground electronic state to long-lived Rydberg states with principal quantum numbers between 39 and 48 using a resonance-enhanced two-color three-photon excitation scheme. The Rydberg states populated had static electric dipole moments exceeding $5000$ D which allowed deceleration of the molecules to rest in the laboratory-fixed frame of reference and three-dimensional trapping using inhomogeneous electric fields. The trapped molecules were confined for up to 10 ms, with effective trap decay time constants increasing with principal quantum number, and ranging from 450$μ$s to 700 $μ$s. These observations, and comparison with the results of similar measurements with He atoms, indicate that the decay dynamics of the trapped Rydberg N$_2$ molecules are dominated by spontaneous emission and do not exhibit significant contributions from effects of intramolecular interactions that lead to non-radiative decay.

physics.atom-ph↗

arXiv2022

Probing van der Waals interactions and detecting polar molecules by Förster resonance energy transfer with Rydberg atoms at temperatures below 100 mK

Electric-field-controlled Förster resonance energy transfer (FRET) between Rydberg helium (He) atoms and ground-state ammonia (NH$_3$) molecules has been studied at translational temperatures below 100 mK. The experiments were performed in an intrabeam collision apparatus with pulsed supersonic beams of NH$_3$ seeded in He. A range of Förster resonances, between triplet Rydberg states in He with principal quantum numbers of 38, 39 and 40, and the inversion intervals in NH$_3$ were investigated. Resonance widths as low as $100\pm20$ MHz were observed for Rydberg-Rydberg transitions with electric dipole transition moments of 3270 D. These widths result from binary collisions at a mean center-of-mass speed of $19.3\pm2.6$ m/s. For transitions in which the initially prepared Rydberg states were strongly polarized, with large induced static electric dipole moments, van der Waals interactions between the collision partners increased the resonance widths to $\sim750$ MHz. From measurements of the rate of FRET for the narrowest resonances observed, a density of NH$_3$ of $(9.4\pm0.3)\times10^{9}$ cm$^{-3}$ in the upper ground-state inversion sublevel in the interaction region of the apparatus was determined non-destructively.

physics.atom-ph↗

arXiv2020

Cavity-enhanced Ramsey spectroscopy at a Rydberg-atom-superconducting-circuit interface

The coherent interaction of Rydberg helium atoms with microwave fields in a $λ/4$ superconducting coplanar waveguide resonator has been exploited to probe the spectral characteristics of an individual resonator mode. This was achieved by preparing the atoms in the 1s55s$^3$S$_1$ Rydberg level by resonance enhanced two-color two-photon excitation from the metastable 1s2s$^3$S$_1$ level. The atoms then travelled over the resonator in which the third harmonic microwave field, at a frequency of $ω_{\mathrm{res}}=2π\times19.556$ GHz, drove the two-photon 1s55s$^3$S$_1\rightarrow$1s56s$^3$S$_1$ transition. By injecting a sequence of Ramsey pulses into the resonator, and monitoring the coherent evolution of the Rydberg state population by state-selective pulsed electric field ionization as the frequency of the microwave field was tuned, spectra were recorded that allowed the resonator resonance frequency and quality factor to be determined with the atoms acting as microscopic quantum sensors.

quant-ph↗

arXiv2020

Coupling Rydberg atoms to microwave fields in a superconducting coplanar waveguide resonator

Rydberg helium atoms traveling in pulsed supersonic beams have been coupled to microwave fields in a superconducting coplanar waveguide (CPW) resonator. The atoms were initially prepared in the 1s55s $^3$S$_1$ Rydberg level by two-color two-photon laser excitation from the metastable 1s2s $^3$S$_1$ level. Two-photon microwave transitions between the 1s55s $^3$S$_1$ and 1s56s $^3$S$_1$ levels were then driven by the 19.556 GHz third-harmonic microwave field in a quarter-wave CPW resonator. This superconducting microwave resonator was fabricated from niobium nitride on a silicon substrate and operated at temperatures between 3.65 and 4.30 K. The populations of the Rydberg levels in the experiments were determined by state-selective pulsed electric field ionization. The coherence of the atom-resonator coupling was studied by time-domain measurements of Rabi oscillations.

quant-ph↗

arXiv2020

Slow decay processes of electrostatically trapped Rydberg NO molecules

Nitric oxide (NO) molecules initially traveling at 795 m/s in pulsed supersonic beams have been photoexcited to long-lived hydrogenic Rydberg-Stark states, decelerated and electrostatically trapped in a cryogenically cooled, chip-based transmission-line Rydberg-Stark decelerator. The decelerated and trapped molecules were detected $in$ $situ$ by pulsed electric field ionization. The operation of the decelerator was validated by comparison of the experimental data with the results of numerical calculations of particle trajectories. Studies of the decay of the trapped molecules on timescales up to 1 ms provide new insights into the lifetimes of, and effects of blackbody radiation on, Rydberg states of NO.

physics.chem-ph↗

arXiv2020

Rydberg-State-Resolved Resonant Energy Transfer in Cold Electric-Field-Controlled Intrabeam Collisions of NH$_3$ with Rydberg He Atoms

The resonant transfer of energy from the inversion sublevels in NH$_3$ to He atoms in triplet Rydberg states with principal quantum number $n=38$ has been controlled using electric fields below 15 V/cm in intrabeam collisions at translational temperatures of $\sim1$ K. The experiments were performed in pulsed supersonic beams of NH$_3$ seeded in He at a ratio of 1:19. The He atoms were prepared in the metastable 1s2s $^3$S$_1$ level in a pulsed electric discharge in the trailing part of the beams. The velocity slip between the heavy NH$_3$ and the lighter metastable He was exploited to perform collision studies at center-of-mass collision speeds of $\sim70$ m/s. Resonant energy transfer in the atom-molecule collisions was identified by Rydberg-state-selective electric-field ionization. The experimental data have been compared to a theoretical model of the resonant dipole-dipole interactions between the collision partners based on the impact parameter method.

physics.chem-ph↗

arXiv2019

Microwave spectroscopy of the $1\mathrm{s}n\mathrm{p}\,^3\mathrm{P}_J$ fine structure of high Rydberg states in $^4$He

The $1\mathrm{s}n\mathrm{p}\,^3\mathrm{P}_J$ fine structure of high Rydberg states in helium has been measured by microwave spectroscopy of single-photon transitions from $1\mathrm{s}n\mathrm{s}\,^3\mathrm{S}_1$ levels in pulsed supersonic beams. For states with principal quantum numbers in the range from $n=34$ to 36, the $J = 0 \rightarrow 2$ and $J = 1 \rightarrow 2$ fine structure intervals were both observed. For values of $n$ between 45 and 51 only the larger $J = 0 \rightarrow 2$ interval was resolved. The experimental results are in good agreement with theoretical predictions. Detailed characterization of residual uncancelled electric and magnetic fields in the experimental apparatus, and calculations of the Stark and Zeeman structures of the Rydberg states in weak fields, were used to quantify systematic contributions to the uncertainties in the measurements.

physics.atom-ph↗

arXiv2019

Matter-wave interferometry with atoms in high Rydberg states

Matter-wave interferometry has been performed with helium atoms in high Rydberg states. In the experiments the atoms were prepared in coherent superpositions of Rydberg states with different electric dipole moments. Upon the application of an inhomogeneous electric field, the different forces on these internal state components resulted in the generation of coherent superpositions of momentum states. Using a sequence of microwave and electric field gradient pulses the internal Rydberg states were entangled with the momentum states associated with the external motion of these matter waves. Under these conditions matter-wave interference was observed by monitoring the populations of the Rydberg states as the magnitudes and durations of the pulsed electric field gradients were adjusted. The results of the experiments have been compared to, and are in excellent quantitative agreement with, matter-wave interference patterns calculated for the corresponding pulse sequences. For the Rydberg states used, the spatial extent of the Rydberg electron wavefunction was ~320 nm. Matter-wave interferometry with such giant atoms is of interest in the exploration of the boundary between quantum and classical mechanics. The results presented also open new possibilities for measurements of the acceleration of Rydberg positronium or antihydrogen atoms in the Earth's gravitational field.

physics.atom-ph↗

arXiv2019

Electric Rydberg-atom interferometery

An electric analogue of the longitudinal Stern-Gerlach matter-wave interferometer has been realized for atoms in Rydberg states with high principal quantum number, $n$. The experiments were performed with He atoms prepared in coherent superpositions of the $n=55$ and $n=56$ circular Rydberg states in zero electric field by a $π/2$ pulse of resonant microwave radiation. These atoms were subjected to a pulsed inhomogeneous electric field to generate a superposition of momentum states before a $π$ pulse was applied to invert the internal states. The same pulsed inhomogeneous electric field was then reapplied for a second time to transform the motional states to have equal momenta before a further $π/2$ pulse was employed to interrogate the final Rydberg state populations. This Hahn-echo microwave pulse sequence, interspersed with a pair of equivalent inhomogeneous electric field pulses, yielded two spatially separated matter waves. Interferences between these matter waves were observed as oscillations in the final Rydberg state populations as the amplitude of the pulsed electric field gradients was adjusted.

physics.atom-ph↗

arXiv2019

Confinement of high- and low-field-seeking Rydberg atoms using time-varying inhomogeneous electric fields

Helium atoms in high- and low-field-seeking Rydberg states with linear and quadratic Stark shifts have been confined in two dimensions and guided over a distance of 150 mm using time-varying inhomogeneous electric fields. This was achieved with an electrode structure composed of four parallel cylindrical rods to which voltages were applied to form oscillating and rotating saddle-point fields. These two modes of operation result in time-averaged pseudopotentials that confine samples in high- and low-field-seeking states about the axis of the device. The experimental data have been compared to the results of numerical particle trajectory calculations that include effects of blackbody radiation and electric field ionization. The results highlight important contributions from single-photon blackbody-induced transitions that cause large changes in the principal quantum number of the Rydberg atoms.

physics.atom-ph↗

arXiv2019

Rydberg state ionization dynamics and tunnel ionization rates in strong electric fields

Tunnel ionization rates of triplet Rydberg states in helium with principal quantum numbers close to 37 have been measured in electric fields at the classical ionization threshold of $\sim197$ V/cm. The measurements were performed in the time domain by combining high-resolution continuous-wave laser photoexcitation and pulsed electric field ionization. The observed tunnel ionization rates range from $10^5$ s$^{-1}$ to $10^7$ s$^{-1}$ and have, together with the measured atomic energy-level structure in the corresponding electric fields, been compared to the results of calculations of the eigenvalues of the Hamiltonian matrix describing the atoms in the presence of the fields to which complex absorbing potentials have been introduced. The comparison of the measured tunnel ionization rates with the results of these, and additional calculations for hydrogen-like Rydberg states performed using semi-empirical methods, have allowed the accuracy of these methods of calculation to be tested. For the particular eigenstates studied the measured ionization rates are $\sim~5$ times larger than those obtained from semi-empirical expressions.

physics.atom-ph↗

arXiv2018

Preparation of circular Rydberg states in helium with $n \geq 70$ using a modified version of the crossed-fields method

Circular Rydberg states with $n=70$ have been prepared in helium using a modified version of the crossed-fields method. This approach to the preparation of high-$n$ circular Rydberg states overcomes limitations of the standard crossed-fields method which arise at this, and higher, values of $n$. The experiments were performed with atoms traveling in pulsed supersonic beams that were initially laser photoexcited from the metastable 1s2s$\,^3$S$_1$ level to the 1s73s$\,^3$S$_1$ level by resonance-enhanced two-color two-photon excitation in a magnetic field of 16.154 G. These excited atoms were then polarized using a perpendicular electric field of 0.844~V/cm, and transferred by a pulse of microwave radiation to the state that, when adiabatically depolarized, evolves into the $n=70$ circular state in zero electric field. The excited atoms were detected by state-selective electric field ionization. Each step of the circular state preparation process was validated by comparison with the calculated atomic energy level structure in the perpendicular electric and magnetic fields used. Of the atoms initially excited to the 1s73s$\,^3$S$_1$ level, $\sim80$\% were transferred to the $n=70$ circular state. At these high values of $n$, $Δn = 1$ circular-to-circular Rydberg state transitions occur at frequencies below 20 GHz. Consequently, atoms in these states, and the circular state preparation process presented here, are well suited to hybrid cavity QED experiments with Rydberg atoms and superconducting microwave circuits.

physics.atom-ph↗

arXiv2018

Probing resonant energy transfer in collisions of ammonia with Rydberg helium atoms by microwave spectroscopy

We present the results of experiments demonstrating the spectroscopic detection of Förster resonance energy transfer from NH$_3$ in the $X\,^1A_1$ ground electronic state to helium atoms in 1s$n$s\,$^3$S$_1$ Rydberg levels, where $n=37$ and $n=40$. For these values of $n$ the 1s$n$s\,$^3$S$_1\rightarrow$1s$n$p\,$^3$P$_J$ transitions in helium lie close to resonance with the ground-state inversion transitions in NH$_3$, and can be tuned through resonance using electric fields of less than 10~V/cm. In the experiments, energy transfer was detected by direct state-selective electric field ionization of the $^3$S$_1$ and $^3$P$_J$ Rydberg levels, and by monitoring the population of the $^3$D$_J$ levels following pulsed microwave transfer from the $^3$P$_J$ levels. Detection by microwave spectroscopic methods represents a highly state selective, low-background approach to probing the collisional energy transfer process and the environment in which the atom-molecule interactions occur. The experimentally observed electric-field dependence of the resonant energy transfer process, probed both by direct electric field ionization and by microwave transfer, agrees well with the results of calculations preformed using a simple theoretical model of the energy transfer process. For measurements performed in zero electric field with atoms prepared in the 1s40s\,$^3$S$_1$ level the transition from a regime in which a single energy transfer channel can be isolated for detection to one in which multiple collision channels begin to play a role has been identified as the NH$_3$ density was increased.

physics.chem-ph↗

arXiv2017

Experimental demonstration of a Rydberg-atom beam splitter

Inhomogeneous electric fields generated above two-dimensional electrode structures have been used to transversely split beams of helium Rydberg atoms into pairs of spatially separated components. The atomic beams had initial longitudinal speeds of between 1700 and 2000 m/s and were prepared in Rydberg states with principle quantum number $n=52$ and electric dipole moments of up to 8700 D by resonance-enhanced two-color two-photon laser excitation from the metastable 1s2s $^3$S$_1$ level. Upon exiting the beam splitter the ensembles of Rydberg atoms were separated by up to 15.6 mm and were detected by pulsed electric field ionization. Effects of amplitude modulation of the electric fields of the beam splitter were shown to cause particle losses through transitions into unconfined Rydberg-Stark states.

physics.atom-ph↗

arXiv2017

Electrically tuned Förster resonances in collisions of NH$_3$ with Rydberg He atoms

Effects of weak electric fields on resonant energy transfer between NH$_3$ in the X $^1$A$_1$ ground electronic state, and Rydberg He atoms in triplet states with principal quantum numbers $n = 36$-$41$ have been studied in a crossed beam apparatus. For these values of $n$, electric-dipole transitions between the Rydberg states that evolve adiabatically to the $|ns\rangle$ and $|np\rangle$ states in zero electric field can be tuned into resonance with the ground-state inversion transitions in NH$_3$ using electric fields, with energy transfer occurring via Förster resonance. In the experiments the Rydberg He atoms, traveling in pulsed supersonic beams, were prepared by resonant two-photon excitation from the metastable $1s2s\,^3S_1$ level and crossed an effusive beam of NH$_3$ before being detected by state-selective pulsed-electric-field ionization. The resonant-energy-transfer process was identified by monitoring changes in the ionization signal from the $|ns\rangle$ and $|np\rangle$ Rydberg states for each value of $n$. The electric field dependence of the experimental data is in good agreement with the results of calculations in which the resonant dipole-dipole coupling between the collision partners was accounted for.

physics.atom-ph↗