Laser cooling and control of excitations in superfluid helium

Harris, Glen I.; McAuslan, David L.; Sheridan, Eoin; Sachkou, Yauhen; Baker, Christopher G.; Bowen, Warwick P.

doi:10.1038/nphys3714

Cited by 72 publications

(169 citation statements)

References 38 publications

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“…By uncovering the nature of the clustering transition in a bounded domain, our theory gives a treatment of the transition relevant for experimental realization in Bose-Einstein condensates, and suggests future directions for testing ensemble equivalence in systems with long-range interactions. Our approach could be extended to arbitrary confining geometries, and provides a starting point for studying vortex clustering phenomena in quantum fluid systems that are strongly forced and damped [86,87].…”

Section: Discussionmentioning

confidence: 99%

Theory of the vortex-clustering transition in a confined two-dimensional quantum fluid

Billam

Nian

et al. 2016

Phys. Rev. A

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Clustering of like-sign vortices in a planar bounded domain is known to occur at negative temperature, a phenomenon that Onsager demonstrated to be a consequence of bounded phase space. In a confined superfluid, quantized vortices can support such an ordered phase, provided they evolve as an almost isolated subsystem containing sufficient energy. A detailed theoretical understanding of the statistical mechanics of such states thus requires a microcanonical approach. Here we develop an analytical theory of the vortex clustering transition in a neutral system of quantum vortices confined to a two-dimensional disk geometry, within the microcanonical ensemble. The choice of ensemble is essential for identifying the correct thermodynamic limit of the system, enabling a rigorous description of clustering in the language of critical phenomena. As the system energy increases above a critical value, the system develops global order via the emergence of a macroscopic dipole structure from the homogeneous phase of vortices, spontaneously breaking the Z 2 symmetry associated with invariance under vortex circulation exchange, and the rotational SO(2) symmetry due to the disk geometry. The dipole structure emerges characterized by the continuous growth of the macroscopic dipole moment which serves as a global order parameter, resembling a continuous phase transition. The critical temperature of the transition, and the critical exponent associated with the dipole moment, are obtained exactly within mean-field theory. The clustering transition is shown to be distinct from the final state reached at high energy, known as supercondensation. The dipole moment develops via two macroscopic vortex clusters and the cluster locations are found analytically, both near the clustering transition and in the supercondensation limit. The microcanonical theory shows excellent agreement with Monte Carlo simulations, and signatures of the transition are apparent even for a modest system of 100 vortices, accessible in current Bose-Einstein condensate experiments.

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Section: Discussionmentioning

confidence: 99%

Theory of the vortex-clustering transition in a confined two-dimensional quantum fluid

Billam

Nian

et al. 2016

Phys. Rev. A

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“…This gas pressure is specifically chosen to provide a superfluid film with a thickness such that the characteristic frequencies of third sound modes intrinsic to the superfluid film [35] do not overlap with the microtoroid mode. At 850 mK the helium transitions directly from the gas phase to its superfluid state, forming a thin (< 5 nm) superfluid layer over the chamber and its contents.…”

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confidence: 99%

“…1(b). A microtoroidal resonator is covered in a several-nanometerthick film of superfluid helium [35], which forms naturally due to van der Waals forces. Absorption of the circulating laser field at the microtoroid periphery (red glow) causes localized heating.…”

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confidence: 99%

Microphotonic Forces from Superfluid Flow

et al. 2016

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In cavity optomechanics, radiation pressure and photothermal forces are widely utilized to cool and control micromechanical motion, with applications ranging from precision sensing and quantum information to fundamental science. Here, we realize an alternative approach to optical forcing based on superfluid flow and evaporation in response to optical heating. We demonstrate optical forcing of the motion of a cryogenic microtoroidal resonator at a level of 1.46 nN, roughly 1 order of magnitude larger than the radiation pressure force. We use this force to feedback cool the motion of a microtoroid mechanical mode to 137 mK. The photoconvective forces we demonstrate here provide a new tool for high bandwidth control of mechanical motion in cryogenic conditions, while the ability to apply forces remotely, combined with the persistence of flow in superfluids, offers the prospect for new applications. DOI: 10.1103/PhysRevX.6.021012 Subject Areas: Photonics, Quantum Physics, SuperfluidityOptical forces are widely utilized in photonic circuits [1,2], micromanipulation [3,4], and biophysics [5,6]. In cavity optomechanics, in particular, optical forces enable cooling and control of microscale mechanical oscillators that can be used for ultrasensitive detection of forces, fields and mass [7][8][9], quantum and classical information systems [10], and fundamental science [11,12]. Recent progress has seen radiation pressure used for coherent state swapping [13], ponderomotive squeezing [14], and ground state cooling [15], while static gradient forces have enabled all-optical routing [16] and nonvolatile mechanical memories [17]. Likewise, photothermal forces, where the mechanical element moves in response to mechanical stress from localized optical absorption and heating, have been used to demonstrate cavity cooling of a semiconductor membrane [18,19], single molecule force spectroscopy [20], and rich chaotic dynamics in suspended mirrors [21].Here, we demonstrate an alternative photoconvective approach to optical forcing that allows an order-ofmagnitude stronger mechanical actuation than radiation pressure. In our implementation, this technique utilizes the convection in superfluids, whereby frictionless fluid flow is generated in response to a local heat source. This well-known superfluid fountain effect [22] is a direct manifestation of the phenomenological two-fluid model proposed by Landau [23] and Tisza [24]. The momentum carried by the helium-4 flow is then transferred to a mechanical element via collision and recoil of superfluid atoms. If the heat source is localized upon the mechanical element, the incident superfluid atoms are either converted to a normal fluid counterflow or evaporated [see Figs. 1(a) and 1(b)]. Alternatively, a distant heat source could be utilized with the mechanical element acting to reroute the superflow.Strong actuation forces are important for a range of techniques in quantum optomechanics, and, most particularly, for protocols that utilize precise measurements combined with feedback act...

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“…Liquid-based optomechanical devices can also be realized by filling [21][22][23][24] or coating [25] a solid electromagnetic cavity with a fluid. In this case only the mechanical degree of freedom is provided by the fluid, for example, as a density wave or surface wave that detunes the cavity by modulating the overlap between the liquid and the cavity mode.…”

Section: Introductionmentioning

confidence: 99%

“…In this case only the mechanical degree of freedom is provided by the fluid, for example, as a density wave or surface wave that detunes the cavity by modulating the overlap between the liquid and the cavity mode. This approach has been used at cryogenic temperatures with superfluid 4 He serving as the liquid [22][23][24][25][26].…”

Section: Introductionmentioning

confidence: 99%

Cavity optomechanics in a levitated helium drop

et al. 2017

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We describe a proposal for a type of optomechanical system based on a drop of liquid helium that is magnetically levitated in vacuum. In the proposed device, the drop would serve three roles: its optical whispering-gallery modes would provide the optical cavity, its surface vibrations would constitute the mechanical element, and evaporation of He atoms from its surface would provide continuous refrigeration. We analyze the feasibility of such a system in light of previous experimental demonstrations of its essential components: magnetic levitation of mm-scale and cm-scale drops of liquid He, evaporative cooling of He droplets in vacuum, and coupling to high-quality optical whispering-gallery modes in a wide range of liquids. We find that the combination of these features could result in a device that approaches the single-photon strong-coupling regime, due to the high optical quality factors attainable at low temperatures. Moreover, the system offers a unique opportunity to use optical techniques to study the motion of a superfluid that is freely levitating in vacuum (in the case of 4 He). Alternatively, for a normal fluid drop of 3 He, we propose to exploit the coupling between the drop's rotations and vibrations to perform quantum nondemolition measurements of angular momentum.

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Laser cooling and control of excitations in superfluid helium

Cited by 72 publications

References 38 publications

Theory of the vortex-clustering transition in a confined two-dimensional quantum fluid

Theory of the vortex-clustering transition in a confined two-dimensional quantum fluid

Microphotonic Forces from Superfluid Flow

Cavity optomechanics in a levitated helium drop

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