Cold Collision Frequency Shift in Two-Dimensional Atomic Hydrogen

Ahokas, J.; Järvinen, J.; Vasiliev, S.

doi:10.1103/physrevlett.98.043004

Cited by 16 publications

(42 citation statements)

References 25 publications

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“…Despite this quantitative understanding of dilute hydrogen, experiments on spin-polarized hydrogen adsorbed on a helium film display a cold collision frequency shift that is two orders of magnitude smaller than theory predicts [213]. This suggests that the helium, though traditionally considered inert, significantly affects the hydrogen.…”

Section: Resultsmentioning

confidence: 85%

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Quantum Phase Transitions in Cold Atoms and Low Temperature Solids

Hazzard¹

2011

Springer Theses

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This thesis describes how to create and probe novel phases of matter and exotic (non-quasiparticle) behavior in cold atomic gases. It focuses on situations whose physics is relevant to condensed matter systems, and where open questions about these latter systems can be addressed. It also attempts to better understand several experimental anomalies in condensed matter systems.The thesis is divided into five parts. The first section or chapter of each part gives an introduction to the motivation and background for the physics of that part; the last section or chapter gives an outlook for future studies. Parts 1-4 (Chapters 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, and 15) introduce and show different facets of how to learn about novel physics relevant to condensed matter using cold atomic systems. Part 5 ( Chapters 16, 17, 18, and 19) constrains explanations of several ill-understood phenomena occurring in low-temperature quantum solids and condensed matter systems and attempts to construct mechanisms for their behavior.Part 1 (Chapters 1 and 2) generally motivates and introduces condensed matter, cold atoms, and many-body physics. Part 2 (Chapters 3, 4, 5, 6, and 7) introduces optical lattice physics and describes ways of spectroscopically probing many-body physics, especially dynamics, near quantum phase transitions in these systems. Part 3 (Chapters 8, 9, 10, 11, and 12) discusses the effects of rotation and how this can create exotic states, as well as alternative methods of creating exotic states. This leads us to study optical lattices where particles possess non-trivial correlations between particles even within a site in Chapters 10 and 11. Part 4 (Chapters 13, 14, and 15) introduces another route to studying exotic physics in cold atoms: examining finite temperature behavior near second order quantum phase transitions. In the "quantum critical regime" occurring near these transitions, non-quasiparticle behavior generically manifests. This behavior has been hidden in previous analyses of data, but Chapter 14 introduces a set of tools required to extract universal quantum critical behavior from standard observables in cold atoms experiments. Chapter 15 discusses near-term opportunities to use these tools to impact fundamental, open questions in condensed matter physics.Part 5 (Chapters 16, 17, 18, and 19) introduces several anomalous or interesting experimental results from low-temperature and solid state physics, constrains possible explanations, and attempts to construct mechanisms for their behavior.Chapter 17 shows that collisional properties between quasi-two-dimensional spinpolarized hydrogen atoms are dramatically modified by the presence of a helium film, on which they are invariably adsorbed in present experiments. Chapter 18 constrains theories regarding recent observations on atomic hydrogen defects in molecular hydrogen quantum solids. Finally, Chapter 19 proposes a mechanism for supersolidity that could account for the experimental observations at that time.Since then, it probably has been...

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Section: Resultsmentioning

confidence: 85%

“…Experimental details.-Ahokas et al [213] study a 2D hydrogen gas bound by van der Waals forces at a distance ζ ∼ 5Å above a helium film, working in a uniform magnetic field B = 4.6T . They produce a cloud with more than 99% of the atoms initially in the lowest hyperfine state |1 .…”

Section: Resultsmentioning

confidence: 99%

Quantum Phase Transitions in Cold Atoms and Low Temperature Solids

Hazzard¹

2011

Springer Theses

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“…Following Ref. [1]'s discussion, the characteristic length scale for the confinement in their experiments is l 0 = √ 2πℓ = 1/ √ 2mE a ∼ 5Å where E a is the adsorption energy of the hydrogen on the helium film. The spectral shift is then…”

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confidence: 93%

“…In Ref. [1], a combination of electron spin resonance and nuclear magnetic resonance drives the transition. In the rotating wave approximation the probe beam's Hamiltonian [11] is H P = Ω P k e −i(ω−(µ2−µ1))t ψ † 2,k ψ 1,k + H.c.…”

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confidence: 99%

Influence of Film-Mediated Interactions on the Microwave and Radio Frequency Spectrum of Spin-Polarized Hydrogen on Helium Films

Hazzard

Mueller

2008

Phys. Rev. Lett.

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We show that helium film-mediated hydrogen-hydrogen interactions account for a two orders of magnitude discrepancy between previous theory and recent experiments on cold collision shifts in spin-polarized hydrogen adsorbed on a helium film. These attractive interactions also explain the anomalous dependence of the cold collision frequency shifts on the 3 He covering of the film. Our findings suggest that the gas will become mechanically unstable before reaching the KosterlitzThouless transition unless the experiment is performed in a drastically different regime, for example with a much different helium film geometry.PACS numbers: 67.63. Gh, 32.30.Bv, 67.25.bh, 32.70.Jz Two-dimensional (2d) spin polarized hydrogen is an exciting quantum fluid. It can support a superfluidnormal Kosterlitz-Thouless transition, which crosses over to Bose-Einstein condensation as the third-dimensional trapping is varied. Hydrogen experiments are unique in involving techniques from both low-temperature physics and atomic physics. The large particle numbers and light mass give a high Bose-Einstein condensation temperature, and the interaction properties are known to high accuracy.In this context, it is remarkable that experiments on spin-polarized hydrogen adsorbed on a helium film display a cold collision frequency shift which is two orders of magnitude smaller than theory predicts [1]. Here we show that a helium mediated interaction can explain this discrepancy and a similarly unexpected dependence of the shift on the concentration of 3 He in the film. Since these experiments are in the "cold collision" regime [2], where the thermal de Broglie wavelength is longer than the interaction's effective range, they see extremely sharp spectral lines which are shifted by interactions. These shifts are important: they limit hydrogen maser [3,4] and atomic fountain [5] performance; the 1S-2S spectral shift first demonstrated Bose-Einstein condensation in hydrogen [6]; the Mott insulator-superfluid phase transition was probed in atomic gases in optical lattices [7,8]; and the shifts revealed features of two-component Fermi gases across a Feshbach resonance [9,10]. Such spectra are promising probes of future strongly-correlated atomic systems.Calculating spectra.-Letting |ij be the state with electron spin i and nuclear spin j, the relevant hydrogen spin states in the experimental B = 4.6T field are |1 ≡ cos θ |↓↑ − sin θ |↑↓ and |2 ≡ cos θ |↑↓ + sin θ |↓↑ with θ negligible. Initially all of the atoms are in state |1 . Neglecting, for now, the helium film's degrees of freedom, the quasi-2d hydrogen's Hamiltonian iswith ψ † j,k bosonic creation operators for states of momentum k and internal state j; ǫ j,k = k 2 /2m + δ j − µ j the free dispersion of the effectively 2d gas, including the internal energy δ j and chemical potential µ j ; and V ij,k the Fourier space interaction potential between atoms in states i and j. Throughout we set = 1.The spectrum is measured by counting the number of atoms transferred from state |1 to state |2 after app...

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“…9 Adsorption of H↓ on the surface of liquid 4 He has been extensively studied because of its optimal properties. [10][11][12][13][14][15] On the one hand, the interaction of any adsorbant with the 4 He surface is the smallest known, and on the other hand, at temperatures T < 300 mK the 4 He vapor pressure is negligible and thereby above the free surface one can reasonably assume vacuum. In fact, liquid 4 He was also extensively used in search of the three-dimensional (3D) H↓ BEC state when the cells were coated with helium films to avoid adsorption of H↓ on the walls and the subsequent recombination to form molecular hydrogen H 2 .…”

Section: Introductionmentioning

confidence: 99%

Spin-polarized hydrogen adsorbed on the surface of superfluid 4He

Marı́n

Markić

Boronat

2013

The Journal of Chemical Physics

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The experimental realization of a thin layer of spin-polarized hydrogen H↓ adsorbed on top of the surface of superfluid 4 He provides one of the best examples of a stable, nearly two-dimensional (2D) quantum Bose gas. We report a theoretical study of this system using quantum Monte Carlo methods in the limit of zero temperature. Using the full Hamiltonian of the system, composed of a superfluid 4 He slab and the adsorbed H↓ layer, we calculate the main properties of its ground state using accurate models for the pair interatomic potentials. Comparing the results for the layer with the ones obtained for a strictly 2D setup, we analyze the departure from the 2D character when the density increases. Only when the coverage is rather small the use of a purely 2D model is justified. The condensate fraction of the layer is significantly larger than in 2D at the same surface density, being as large as 60% at the largest coverage studied. © 2013 AIP Publishing LLC.

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Cold Collision Frequency Shift in Two-Dimensional Atomic Hydrogen

Cited by 16 publications

References 25 publications

Quantum Phase Transitions in Cold Atoms and Low Temperature Solids

Quantum Phase Transitions in Cold Atoms and Low Temperature Solids

Influence of Film-Mediated Interactions on the Microwave and Radio Frequency Spectrum of Spin-Polarized Hydrogen on Helium Films

Spin-polarized hydrogen adsorbed on the surface of superfluid 4He

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