arXiv subjects

Alexander Guttridge

Publications and source records attributed to Alexander Guttridge.

14 recordsLinked to original sources

arXiv2026

Harnessing resonant dipolar interactions in a hybrid atom-molecule quantum system

Hybrid quantum systems offer a route to combining the complementary strengths of distinct quantum platforms while mitigating their limitations. A particularly promising architecture combines neutral atoms and polar molecules: atoms provide fast, controllable interactions through excitation to Rydberg states, while molecules possess long-lived rotational states that are attractive for quantum memories and qudits. Although dipolar interactions between atoms and molecules have been observed in gas-phase and beam experiments, they have not previously been explored in a scalable optical tweezer platform that enables the controlled coherent interactions needed for quantum state transfer and entanglement. Here, we realise this goal, demonstrating coherent dipolar interactions between an individual Rydberg atom and an individual polar molecule. The separation of the particles is controlled using species-specific optical tweezers and their dipolar interactions are made strongly state-dependent by tuning two atom-molecule pair states into resonance. We exploit these interactions to demonstrate atom-mediated state readout of a molecular qubit, observe coherent spin exchange between the particles, and generate entanglement using a blockade-based controlled-NOT operation. Together, these results establish a coherent atom-molecule interface in which long-lived molecular quantum information can be rapidly mapped onto internal states of a Rydberg atom for readout or onward coherent transfer. This platform can be scaled to realise hybrid quantum processors utilising atom-mediated readout and entanglement of molecular qubits and mixed-species quantum simulators of dipolar systems.

physics.atom-ph↗

arXiv2024

Long-lived multilevel coherences and spin-1 dynamics encoded in the rotational states of ultracold molecules

Rotational states of ultracold polar molecules possess long radiative lifetimes, microwave-domain coupling, and tunable dipolar interactions. The availability of numerous rotational states has inspired many proposed applications, including simulations of quantum magnetism, encodings of information in high-dimensional qudits, and synthetic dimensions with many synthetic lattice sites. Many of these applications are yet to be realised, primarily because engineering long-lived coherent superpositions of multiple rotational states is highly challenging. Here, we investigate how multilevel coherences between rotational states can be engineered by using optical tweezer traps operating close to a magic wavelength for a given pair of states. By performing precision Ramsey spectroscopy we find the exact magic wavelengths and sensitivities to detuning errors for multiple rotational state superpositions. We find that, for a trap polarised parallel to the quantisation axis, the magic wavelengths are closely clustered enabling long-lived coherence across multiple rotational states simultaneously. As an example, we demonstrate simultaneous second-scale coherence between three rotational states. Utilising this extended coherence, we perform multiparameter estimation using a generalised Ramsey sequence and demonstrate coherent spin-1 dynamics encoded in the rotational states. With modest experimental improvements, we predict that second-scale coherent dynamics of ten rotational states should be readily achievable.

physics.atom-ph↗

arXiv2024

Individual assembly of two-species Rydberg molecules using optical tweezers

We present a new approach to investigating Rydberg molecules by demonstrating the formation and characterization of individual Rb$^{*}$Cs Rydberg molecules using optical tweezers. By employing single-atom detection of Rb and Cs, we observe molecule formation via correlated loss of both species and study the formation dynamics with single-particle resolution. We control the interatomic distances by manipulating the relative wavefunction of atom pairs using the tweezer intensity, optimizing the coupling to molecular states and exploring the effect of the tweezer on these states. Additionally, we demonstrate molecule association with atoms trapped in separate tweezers, paving the way for state-selective assembly of polyatomic molecules. The observed binding energies, molecular alignment, and bond lengths are in good agreement with theory. Our approach is broadly applicable to Rydberg tweezer platforms, expanding the range of available molecular systems and enabling the integration of Rydberg molecules into existing quantum science platforms.

physics.atom-ph↗

arXiv2024

Long-lived entanglement of molecules in magic-wavelength optical tweezers

Realising quantum control and entanglement of particles is crucial for advancing both quantum technologies and fundamental science. Significant developments in this domain have been achieved in a variety of systems. In this context, ultracold polar molecules offer new and unique opportunities due to their more complex internal structure associated with vibration and rotation, coupled to the existence of long-range interactions. However, the same properties make molecules highly sensitive to their environment, impacting their coherence and utility in some applications. Here we show that by engineering an exceptionally controlled environment using rotationally-magic optical tweezers, we can achieve long-lived entanglement between pairs of molecules using hertz-scale interactions. We demonstrate the highest reported fidelity to date for a two-molecule Bell state ($0.976^{+0.014}_{-0.016}$) and present the first realisation of a microwave-driven entangling gate between two molecules, preparing the molecules in a decoherence-free subspace. We show that the magic-wavelength trap preserves the entanglement, with no measurable decay over 0.5 s, opening new avenues for quantum-enhanced metrology, ultracold chemistry and the use of rotational states for quantum simulation, quantum computation and as quantum memories. The extension of precise quantum control to complex molecular systems will allow their additional degrees of freedom to be exploited across many domains of quantum science.

physics.atom-ph↗

arXiv2024

Enhanced quantum state transfer via feedforward cancellation of optical phase noise

Many experimental platforms for quantum science depend on state control via laser fields. Frequently, however, the control fidelity is limited by optical phase noise. This is exacerbated in stabilized laser systems where high-frequency phase noise is an unavoidable consequence of feedback. Here we implement an optical feedforward technique to suppress laser phase noise in the STIRAP state transfer of ultracold RbCs molecules, across 114 THz, from a weakly bound Feshbach state to the rovibrational ground state. By performing over 100 state transfers on single molecules, we measure a significantly enhanced transfer efficiency of 98.7(1)% limited only by available laser intensity.

quant-ph↗

arXiv2024

Enhanced quantum control of individual ultracold molecules using optical tweezer arrays

Control over the quantum states of individual molecules is crucial in the quest to harness their rich internal structure and dipolar interactions for applications in quantum science. In this paper, we develop a toolbox of techniques for the control and readout of individually trapped polar molecules in an array of optical tweezers. Starting with arrays of up to eight Rb and eight Cs atoms, we assemble arrays of RbCs molecules in their rovibrational and hyperfine ground state with an overall efficiency of 48(2)%. We demonstrate global microwave control of multiple rotational states of the molecules and use an auxiliary tweezer array to implement site-resolved addressing and state control. We show how the rotational state of the molecule can be mapped onto the position of Rb atoms and use this capability to readout multiple rotational states in a single experimental run. Further, using a scheme for the mid-sequence detection of molecule formation errors, we perform rearrangement of assembled molecules to prepare small defect-free arrays. Finally, we discuss a feasible route to scaling to larger arrays of molecules.

physics.atom-ph↗

arXiv2024

Ultralong-range Cs-RbCs Rydberg molecules: non-adiabaticity of dipole moments

We consider ultralong-range polyatomic Rydberg molecules formed by combining a Rydberg cesium atom and a ground-state RbCs molecule. We explore the regime where the charge-dipole interaction due to the Rydberg electron with the diatomic polar molecule couples the quantum defect Rydberg states Cs(ns) to the nearest degenerate hydrogenic manifold. We consider polyatomic Rydberg molecules in states which are amenable to production in optical tweezers and study the influence of nonadiabatic coupling on the likelihood of their formation. The decay rates of the vibrational states reflect the interference signature of wave function spread in different coupled potential wells.

physics.atom-ph↗

arXiv2023

Observation of Rydberg blockade due to the charge-dipole interaction between an atom and a polar molecule

We demonstrate Rydberg blockade due to the charge-dipole interaction between a single Rb atom and a single RbCs molecule confined in optical tweezers. The molecule is formed by magnetoassociation of a Rb+Cs atom pair and subsequently transferred to the rovibrational ground state with an efficiency of 91(1)\%. Species-specific tweezers are used to control the separation between the atom and molecule. The charge-dipole interaction causes blockade of the transition to the Rb(52s) Rydberg state, when the atom-molecule separation is set to $310(40)$~nm. The observed excitation dynamics are in good agreement with simulations using calculated interaction potentials. Our results open up the prospect of a hybrid platform where quantum information is transferred between individually trapped molecules using Rydberg atoms.

physics.atom-ph↗

arXiv2023

Formation of ultracold molecules by merging optical tweezers

We demonstrate the formation of a single RbCs molecule during the merging of two optical tweezers, one containing a single Rb atom and the other a single Cs atom. Both atoms are initially predominantly in the motional ground states of their respective tweezers. We confirm molecule formation and establish the state of the molecule formed by measuring its binding energy. We find that the probability of molecule formation can be controlled by tuning the confinement of the traps during the merging process, in good agreement with coupled-channel calculations. We show that the conversion efficiency from atoms to molecules using this technique is comparable to magnetoassociation.

physics.atom-ph↗

arXiv2022

Observation of magnetic Feshbach resonances between Cs and ${}^{173}$Yb

We report the first observation of magnetic Feshbach resonances between ${}^{173}$Yb and $^{133}$Cs. In a mixture of Cs atoms prepared in the $(f=3, m_f=3)$ state and unpolarized fermionic ${}^{173}$Yb we observe resonant atom loss due to two sets of magnetic Feshbach resonances around 622~G and 702~G. Resonances for individual Yb nuclear spin components $m_{i,\mathrm{Yb}}$ are split by its interaction with the Cs electronic spin, which also provides the main coupling mechanism for the observed resonances. The observed splittings and relative resonance strengths are in good agreement with theoretical predictions from coupled-channel calculations.

physics.atom-ph↗

arXiv2021

Quantum Degenerate Mixtures of Cs and Yb

We report the production of quantum degenerate Bose-Bose mixtures of Cs and Yb with both attractive (Cs + $^{174}$Yb) and repulsive (Cs + $^{170}$Yb) interspecies interactions. Dual-species evaporation is performed in a bichromatic optical dipole trap that combines light at 1070 nm and 532 nm to enable control of the relative trap depths for Cs and Yb. Maintaining a trap which is shallower for Yb throughout the evaporation leads to highly efficient sympathetic cooling of Cs for both isotopic combinations at magnetic fields close to the Efimov minimum in the Cs three-body recombination rate at around 22 G. For Cs + $^{174}$Yb, we produce quantum mixtures with typical atom numbers of $N_\mathrm{Yb} \sim 5 \times 10^4$ and $N_\mathrm{Cs} \sim 5 \times 10^3$. We find that the attractive interspecies interaction (characterised by the scattering length $a_\mathrm{CsYb} = -75\,a_0$) is stabilised by the repulsive intraspecies interactions. For Cs + $^{170}$Yb, we produce quantum mixtures with typical atom numbers of $N_\mathrm{Yb} \sim 4 \times 10^4$, and $N_\mathrm{Cs} \sim 1 \times 10^4$. Here, the repulsive interspecies interaction ($a_\mathrm{CsYb} = 96\,a_0$) can overwhelm the intraspecies interactions, such that the mixture sits in a region of partial miscibility.

cond-mat.quant-gas↗

arXiv2020

Dynamics of a degenerate Cs-Yb mixture with attractive interspecies interactions

We probe the collective dynamics of a quantum degenerate Bose-Bose mixture of Cs and $^{174}$Yb with attractive interspecies interactions. Specifically, we excite vertical center of mass oscillations of the Cs condensate, and observe significant damping for the Cs dipole mode, due to the rapid transfer of energy to the larger Yb component, and the ensuing acoustic dissipation. Numerical simulations based on coupled Gross-Pitaevskii equations provide excellent agreement, and additionally reveal the possibility of late-time revivals (beating) which are found to be highly sensitive to the Cs and Yb atom number combinations. By further tuning the interaction strength of Cs using a broad Feshbach resonance, we explore the stability of the degenerate mixture, and observe collapse of the Cs condensate mediated by the attractive Cs-Yb interaction when $a_{\mathrm{Cs}}<50 \, a_0$, well above the single-species collapse threshold, in good agreement with simulations.

cond-mat.quant-gas↗

arXiv2018

Two-photon photoassociation spectroscopy of CsYb: ground-state interaction potential and interspecies scattering lengths

We perform two-photon photoassociation spectroscopy of the heteronuclear CsYb molecule to measure the binding energies of near-threshold vibrational levels of the $X~^{2}Σ_{1/2}^{+}$ molecular ground state. We report results for $^{133}$Cs$^{170}$Yb, $^{133}$Cs$^{173}$Yb and $^{133}$Cs$^{174}$Yb, in each case determining the energy of several vibrational levels including the least-bound state. We fit an interaction potential based on electronic structure calculations to the binding energies for all three isotopologs and find that the ground-state potential supports 77 vibrational levels. We use the fitted potential to predict the interspecies s-wave scattering lengths for all seven Cs+Yb isotopic mixtures.

physics.atom-ph↗

arXiv2018

Production of ultracold Cs*Yb molecules by photoassociation

We report the production of ultracold heteronuclear Cs$^*$Yb molecules through one-photon photoassociation applied to an ultracold atomic mixture of Cs and Yb confined in an optical dipole trap. We use trap-loss spectroscopy to detect molecular states below the Cs($^{2}P_{1/2}$) + Yb($^{1}S_{0}$) asymptote. For $^{133}$Cs$^{174}$Yb, we observe 13 rovibrational states with binding energies up to $\sim$500 GHz. For each rovibrational state we observe two resonances associated with the Cs hyperfine structure and show that the hyperfine splitting in the diatomic molecule decreases for more deeply bound states. In addition, we produce ultracold fermionic $^{133}$Cs$^{173}$Yb and bosonic $^{133}$Cs$^{172}$Yb and $^{133}$Cs$^{170}$Yb molecules. From mass scaling, we determine the number of bound states supported by the 2(1/2) excited-state potential to be 154 or 155.

physics.atom-ph↗