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Overview

Theo Murphy meeting organised by Professor Simon Cornish, Professor Michael Tarbutt and Dr Hannah Price. 

Ultracold molecules offer a new and fascinating system for the study of many aspects of quantum science including ultracold chemistry, quantum computing, metrology, quantum simulation and fundamental physics. Following rapid recent progress, this meeting brought the community together to explore synergies with other disciplines and to map out the future avenues of research with ultracold molecules.

Attending this event

This meeting has taken place.

Enquiries: contact the Scientific Programmes team.

Organisers

Schedule


Chair

09:00-09:05
Welcome by the lead organiser
09:05-09:30
Measuring quantum correlations in a many-body system of polar molecules

Abstract

Ultracold molecules have promising applications in the fields of quantum computing and simulation of many-body systems. Central to these applications is the ability to detect and manipulate the quantum state of individual molecules. Professor Bakr and his research group have recently developed a novel apparatus for imaging single diatomic molecules in an ultracold gas prepared in well-defined electronic, rovibrational and hyperfine states. Professor Bakr will describe how they used this capability to measure quantum correlations due to the quantum statistics of the molecules or due to entanglement mediated by dipolar interactions. As an example of a potential application, he will discuss their study of out-of-equilibrium dynamics in tunable quantum spin models and their measurements of the evolution of spatial correlations during the ensuing thermalization process. 

Speakers

09:30-09:45
Discussion
09:45-10:15
Synthetic dimensions in Rydberg atoms and dipolar molecules

Abstract

The many accessible rotational states of molecules or electronic states of Rydberg atoms allow experiments to create synthetic dimensions, mimicking real-space motion by coupling of internal states. This provides extremely flexible engineering of single-particle physics, such as topological band structures, and when combined with dipolar interactions leads to rich physics. Professor Hazzard will describe a pair of recent experiments with Rydberg atom synthetic dimensions: a realisation of topological edge states (Killian & Dunning group, Nature Communications 13, 972 (2022)), and a first demonstration of interacting synthetic dimensions by using tweezer arrays, which is used to explore interacting particles in gauge fields (Gadway/Covey group, in preparation). He will discuss how interactions can lead to a wealth of novel phenomena: quantum strings/membranes, gapless symmetry-protected topological phases, or, dramatically. parastatistical quasiparticles, a type of particle beyond fermions and bosons. The author will conclude with the progress and rich opportunities for molecule synthetic dimensions. 

Speakers

10:15-10:30
Discussion
10:30-11:00
Break
11:00-11:30
Tunable itinerant spin dynamics with dipolar molecules

Abstract

Ultracold molecules enable exploration of exciting many-body physics due to their long-range, anisotropic dipolar interactions that govern dynamics in both internal and external degrees of freedom. Many scientific ideas based on this unique platform are now realizable due to recent experimental advances, including the production of quantum degenerate molecular gases, the shielding of inelastic collisions, the local state preparation and readout, and the precise tuning of a spin Hamiltonian. Annette Carroll will describe the recent study of tunable interactions between itinerant KRb molecules confined to 2D planes. At short times, the motion of the molecules is decoupled from the spin degree of freedom, and the spin dynamics are well-described by the mean field limit of the XXZ Hamiltonian. The mean field interaction, which shifts the rotational transition frequencies, was detected using Ramsey spectroscopy. The interaction’s strength and sign can be tuned with applied electric fields, as well as with the choice of rotational states. At longer times, elastic dipolar collisions, which couple the spin and motion, drive spin decoherence. This work paves the way for investigations of many-body spin-motion effects.

Speakers

11:30-11:45
Discussion
11:45-12:15
Understanding and controlling collisions in quantum gases of NaK molecules

Abstract

In this talk, Professor Ospelkaus will report about their recent experiments with quantum gases of polar bosonic 23Na39K molecules. She will first discuss inelastic atom-molecule and molecule-molecule collisions and their origin [1,2,3]. Afterwards she will discuss the control of atom-molecule collisions by Feshbach resonances as well as a proposal for blue shielding of collisions of polar molecules using optical photons at Raman resonance [4].

[1] Kai K. Voges, Philipp Gersema, Mara Meyer zum Alten Borgloh, Torben A. Schulze, Torsten Hartmann, Alessandro Zenesini, and Silke Ospelkaus (2020): Ultracold Gas of Bosonic 23Na39K Ground-State Molecules,  Physical Review Letters 125, 083401 (2020)
[2] Philipp Gersema, Kai K. Voges, Mara Meyer zum Alten Borgloh, Leon Koch, Torsten Hartmann, Alessandro Zenesini, Silke Ospelkaus, Junyu Lin, Junyu He, and Dajun Wang: Probing photoinduced two-body loss of ultracold non-reactive bosonic 23Na87Rb and 23Na39K molecules,  PRL 127, 163401 (2021)
[3] Kai K. Voges, Philipp Gersema, Torsten Hartmann, Silke Ospelkaus, and Alessandro Zenesini (2022): Hyperfine dependent atom-molecule loss analyzed by the analytic solution of few-body loss equations,  Physical Review Research 4, 023184 (2022)
[4] Charbel Karam, Mara Meyer zum Alten Borgloh, Romain Vexiau, Maxence Lepers, Silke Ospelkaus, Nadia Bouloufa-Maafa, Leon Karpa, Olivier Dulieu: Two-photon optical shielding of collisions between ultracold polar molecules, arxiv:2211.08950

Speakers

12:15-12:30
Discussion
12:30-13:30
Lunch

Chair

13:30-14:00
Optical tweezer arrays of laser-cooled molecules as a new platform for quantum science

Abstract

Molecules, with their rich structure and tunable long-range interactions, have been proposed as a versatile platform for quantum science. In this talk, Professor Cheuk will report on recent advances from our group on controlling laser-cooled molecules that are trapped in optical tweezer arrays. He will describe their work on creating defect-free arrays of CaF molecules in 1D and observing coherent dipolar interactions between molecular pairs, and discuss how these results establish the building blocks for quantum information processing and quantum simulation of spin models using molecular tweezer arrays. Professor Cheuk will also report about their recent work towards full quantum control of laser-cooled molecules trapped in optical tweezers including their motional degrees of freedom. Specifically, he will report on Raman sideband cooling for molecules, and discuss how it provides a new pathway towards creating low-entropy molecular ensembles useful for quantum science.

Speakers

14:00-14:15
Discussion
14:15-14:45
Magic polarisation trapping of polar molecules for tunable dipolar interactions

Abstract

Ultracold polar molecules can interact at long-range via electric dipole-dipole interactions, which can be controlled to entangle distant molecules by coherently coupling their rotational quantum states. Such capability, together with the abundance of rotational quantum states, makes polar molecules attractive for quantum simulation and computation. The author of the talk together with a group of researchers prepare an optical tweezer array of individual NaCs molecules in the ground state of their internal and motional degrees of freedom and perform rotational spectroscopy. In their system, the rotational coherence is predominantly limited by tweezer intensity noise, which induces differential light shifts between rotational states. To circumvent this problem, the researchers employ a new technique that uses 'magic' ellipticity trapping of polar molecules. With this technique, they reduce the differential polarisability by three orders of magnitude and improve the coherence time by an order of magnitude. With < 0.5 μm control over molecule position and site-selective rotational state control, the researchers expect to entangle the two adjacent rotational states within 1 ms.

Speakers

14:45-15:00
Discussion
15:00-15:30
Break
15:30-16:00
Second-scale rotational coherence times in ultracold RbCs molecules

Abstract

Ultracold polar molecules possess a rich network of rotational and hyperfine states that can be precisely coupled in experiments with resonant microwave fields. Engineering long-lived quantum coherences between rotational states is crucial for realising the full potential of ultracold molecules in current experiments. For molecules confined to optical traps, the rotational coherence time is typically limited by to the presence of large differential light shifts between the rotational states as a result of the anisotropic molecular polarisability. Here Dr Gregory will demonstrate a rotationally-magic optical trap for RbCs molecules that supports a Ramsey coherence time of 0.78(4) seconds, which extends to >1.4 seconds at the 95% confidence level using a single spin-echo pulse. In the researcher's magic trap, inhomogeneous and anisotropic dipolar interactions become the dominant source of decoherence, and they show that the coherence time is inversely proportional to the strength of these interactions.

Speakers

16:00-16:15
Discussion
16:15-16:45
Suppression of loss in ultracold NaRb molecules

Abstract

In this presentation, Professor Wang will discuss their recent findings on mitigating the two-body loss of ground-state NaRb molecules. To achieve this, the scientists employ a blue-detuned microwave to create a long-range potential barrier, which significantly decreases the formation of the two-molecule complex, thereby reducing short-range loss by two orders of magnitude. Conversely, they observe a significant increase in elastic collisions, allowing the elastic collision rate to reach the hydrodynamic limit even at relatively low number densities. Additionally, the scientists demonstrate efficient evaporative cooling, but only within a specific density range.

Speakers

16:45-17:00
Discussion
17:00-18:15
Poster session

Chair

09:00-09:30
Quantum simulation of the central spin model with a Rydberg atom and polar molecules in optical tweezers

Abstract

Central spin models, where a single spinful particle interacts with a spin environment, find wide application in quantum information technology and can be used to describe, eg the decoherence of a qubit over time. The authors propose a method of realising an ultracold quantum simulator of a central spin model with XX (spin-exchanging) interactions [1]. The proposed system consists of a single Rydberg atom ("central spin") and surrounding polar molecules ("bath spins"), coupled to each other via dipole-dipole interactions. By mapping internal particle states to spin states, spin-exchanging interactions can be simulated. As an example system geometry, the authors consider a ring-shaped arrangement of bath spins, and show how it allows to exact precise control over the interaction strengths. They demonstrate that this setup allows to realise a central spin model with highly tunable parameters and geometry, for applications in quantum science and technology.

[1] Dobrzyniecki J, Tomza, M 2023. ‘Quantum simulation of the central spin model with a Rydberg atom and polar molecules in optical tweezers,’arXiv:2302.14774v1 [quant-ph]

Speakers

09:30-09:45
Discussion
09:45-10:15
Observation of Rydberg blockade due to the charge-dipole interaction between an atom and a polar molecule

Abstract

Ultracold dipolar systems, including atoms excited to Rydberg states and polar molecules, hold great potential for quantum simulation and computation. Rydberg atoms offer strong, long-range interactions, which enable the engineering of quantum entanglement and multi-qubit gates through the Rydberg blockade mechanism. Polar molecules also exhibit long-range interactions and possess multiple long-lived rotational states that can be coupled using microwave fields to achieve high-fidelity quantum operations. Optical tweezer arrays have enabled the trapping of both these systems, creating the possibility of a hybrid system that combines the advantages of both platforms. This hybrid system offers new capabilities, including non-destructive readout of the molecular state, cooling of molecules using Rydberg atoms, and photoassociation of giant polyatomic Rydberg molecules. 

In this talk, Dr Guttridge will describe the first observation of Rydberg blockade due to the charge-dipole interaction between an atom and a polar molecule. The experiment involves the creation of a hybrid system consisting of ultracold RbCs molecules and Rb atoms trapped in species-specific optical tweezers. The researchers form weakly bound RbCs molecules by merging together optical tweezers containing Rb and Cs molecules. Strikingly, they find that weakly bound molecules can be produced without the widely used method of magnetoassociation across a Feshbach resonance but instead by exploiting an avoided crossing between atomic and molecular states as a function of tweezer separation. They transfer these weakly bound RbCs molecules to the rovibrational ground state using stimulated Raman adiabatic passage and achieve a one-way efficiency of 91(1)%.  Finally, the researchers observe blockade of the transition to the Rb(52s) Rydberg state due to the charge-dipole interaction with a RbCs molecule in the rovibrational ground state. The blockade they have observed provides a mechanism for conditional and non-destructive state readout of the molecule and opens up many new research directions which Dr Guttridge will briefly discuss.

Speakers

10:15-10:30
Discussion
10:30-11:00
Break
11:00-11:30
Quantum engineering of pair production process in spin models in multi- layers: from two- mode squeezing to topological Kitaev models

Abstract

Understanding and controlling the growth and propagation of quantum correlations and entanglement is an emerging frontier in non-equilibrium many-body physics, and a crucial key step for unlocking the full advantage of quantum systems. In this talk Professor Ana Maria Rey will discuss how in multi-layer spin systems, currently accessible in a broad range of quantum platforms, such as arrays of neutral atoms, Rydberg atoms, magnetic atoms and polar molecules, spin interactions can be utilized to realize in a controllable manner  a variety of correlated pair-production processes. In particular, the author will describe how in bi-layer systems, the capability to select individual layers and prepare targeted initial states, can enable the generation of iconic two-mode squeezing models that feature  exponential growth of entanglement and are relevant in many contexts  ranging  from the foundations of quantum mechanics, to parametric amplification in quantum optics, to the Schwinger effect in high energy physics and Unruh thermal radiation in general relativity. In multi-layers the author will show it is possible to engineer a chiral bosonic Kitaev model featuring chiral propagation of correlations. Overall in this talk Professor Ana Maria Rey will  report how current single layer addressing capabilities can allow shaping  and controlling the temporal growth and spatial propagation of quantum correlations in a variety of spin systems relevant for quantum simulation.  

 

Speakers

11:30-11:45
Discussion
11:45-12:15
Degenerate Fermi gases of microwave-shielded polar molecules

Abstract

Stable molecular Fermi gases with strong dipolar interactions provide unique opportunities for studying exotic quantum matter such as p-wave superfluidity and extended Fermi-Hubbard models. Dr Xin-Yu Luo will first show how they prepare a large degenerate Fermi gas of heteronuclear Feshbach molecules [1]. After being transferred to the rovibronic ground state, the scientists stabilize the molecular gas by microwave shielding while inducing strong elastic dipolar collisions. This enables the evaporation of polar molecules to temperatures well below the Fermi temperature [2]. The intermolecular potential can be flexibly tuned by the microwave field, allowing them to observe field-linked resonances in collisions of polar molecules. It provides a universal tuning knob to independently control the dipolar interaction and contact interaction [3]. In the end, Dr Xin-Yu Luo will discuss the perspective of realizing dipolar p-wave superfluidity in polar molecules [4] and their efforts towards further cooling down the molecular gas. 

[1] M. Duda et al, Transition from a polaronic condensate to a degenerate Fermi gas of heteronuclear molecules, Nature Physics 1-6 (2023)
[2] A. Schindewolf et al, Evaporation of microwave-shielded polar molecules to quantum degeneracy, Nature 607, 677 (2022)
[3] X-Y Chen et al, Field-linked resonances of polar molecules, Nature 614, 59 (2023) 
[4] F Deng et al, Effective potential and superfluidity of microwave-dressed polar molecules, arXiv preprint arXiv:2210.13253 (2023)

Speakers

12:15-12:30
Discussion

Chair

13:30-14:00
Ultracold molecules for quantum science and particle physics

Abstract

Polar molecules, due to their intrinsic electric dipole moment and their controllable complexity, are a powerful platform for precision measurement searches for physics beyond the standard model (BSM) and, potentially, for quantum simulation/computation. This has led to many experimental efforts to cool and control molecules at the single quantum state level, including with CaF. Professor Doyle will present work demonstrating entanglement and iSWAP operations with individual CaF molecules in optical tweezers. Polyatomic molecules have attracted new focus as potential novel quantum resources with distinct advantages - and challenges - compared to both atoms and diatomic molecules. He will discuss features of polyatomic molecules that can be used in quantum simulation/computation, the search for BSM physics, and ultracold chemistry. Professor Doyle will discuss the results on the laser cooling of polyatomic molecules into the ultracold regime, including the laser cooling of the polyatomic molecules SrOH, YbOH, CaOH and CaOCH3. Finally, if time permits, he will discuss recent measurements on spin precession in a metastable vibrational bending mode of CaOH, useful for future experiments searching for the electron electric dipole moment, a probe for BSM physics in the >10 TeV range.

Speakers

14:00-14:15
Discussion
14:15-14:45
Laser cooling of YO molecules to achieve high phase-space density

Abstract

Ultracold molecules are a promising platform for precision physics, quantum chemistry, quantum simulation, and quantum information studies. In the last decade, there has been a flurry of interesting activity in the direct laser cooling of molecules, down to temperatures of a few μK. Recently, an optical tweezer array of molecules has been demonstrated. However, owing to the low phase-space density (PSD) of laser cooled polar molecules loaded into conservative traps, collisions in a bulk sample have remained elusive so far, in contrast to ultracold bialkali molecules created via association. Dr Aggarwal’s group is pursuing the goal of reaching quantum degeneracy of YO molecules. 

The PSD in conservative traps is limited largely by inefficient loading (few percent) due to large cloud sizes after sub-doppler cooling of molecules. In this talk, the author will present their recent results on the first sub-Doppler magneto-optical trap (MOT) of YO molecules [1]. The scientists observe volume compression by a factor of ~ 300 and temperature reduction by a factor of ~ 60 down to 30 μK in comparison to a conventional red detuned MOT, reaching a PSD several orders of magnitude higher than any previous molecular MOT. Currently, they are working on another cooling mechanism. YO has a low-lying excited state with a narrow transition linewidth of ~7 kHz. Optical photon scattering on this transition will result in cooling the molecules to recoil temperatures of 100s of nK. Dr Aggarwal will also present their progress so far on the narrow-line cooling of molecules.

[1] Burau et al arXiv 2212.07472 (2022).

Speakers

14:45-15:00
Discussion
15:00-15:30
Break
15:30-16:00
Dipolar interactions of Rydberg atoms with polar molecules and superconducting circuits

Abstract

The large electric dipole moments, ~ 1000 D, associated with transitions between high Rydberg states in atoms and molecules, offer opportunities to exploit resonant electric dipole interactions with polar ground state molecules, and with microwave fields in superconducting circuits for applications in quantum science. 

In this talk Professor Hogan will describe experiments in which resonant energy transfer, arising as a result of electric dipole-dipole interactions between helium Rydberg atoms and cold ground-state ammonia molecules, have been studied at temperatures below 100 mK and controlled using weak electric fields [1,2]. He will also describe experiments in which Rydberg atoms have been coherently coupled to microwave fields in superconducting co-planar waveguide resonators [3] in a setting that may open future opportunities for mediation of dipolar interactions with cold polar molecules over long range for applications in quantum simulation and information processing [4].

[1] K Gawlas and S D Hogan, J Phys Chem Lett 11, 83 (2020)
[2] J Zou and S D Hogan, Phys Rev A 106, 043111 (2022)
[3] A A Morgan and S D Hogan, Phys Rev Lett 124, 193604 (2020)
[4] P Rabl, D DeMille, J M Doyle, M D Lukin, R J Schoelkopf, and P Zoller, Phys Rev Lett 97, 033003 (2006)

Speakers

16:00-16:15
Discussion
16:15-17:00
Panel discussion/overview