Quantum liquids

Glyde, H. R.

doi:10.1088/1361-648x/ab2ba6

Cited by 3 publications

(3 citation statements)

References 82 publications

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“…Subsequently, the outer spectrometer was moved to the N5 through-tube. Much further research into the properties of superfluid liquid He 4 was carried out as summarized by H. Glyde in his contribution to the commemorative volume for Roger Cowley [123]. The most accurate estimate of the superfluid fraction, n 0 = (7.25 ± 0.25)%, is within the error band originally estimated at Chalk River.…”

Section: Epiloguementioning

confidence: 89%

The First Two Decades of Neutron Scattering at the Chalk River Laboratories

Holden

2021

QuBS

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The early advances in neutron scattering at the Chalk River Laboratories of Atomic Energy of Canada are recorded. From initial nuclear physics measurements at the National Research Experimental (NRX) reactor came the realization that, with the flux available and improvements in monochromator technology, direct measurements of the normal modes of vibrations of solids and the structure and dynamics of liquids would be feasible. With further flux increases at the National Research Universal (NRU) reactor, the development of the triple-axis crystal spectrometer, and the invention of the constant-Q technique, the fields of lattice dynamics and magnetism and their interpretation in terms of the long-range forces between atoms and exchange interactions between spins took a major step forward. Experiments were performed over a seven-year period on simple metals such as potassium, complex metals such as lead, transition metals, semiconductors, and alkali halides. These were analyzed in terms of the atomic forces and demonstrated the long-range nature of the forces. The first measurements of spin wave excitations, in magnetite and in the 3D metal alloy CoFe, also came in this period. The first numerical estimates of the superfluid fraction of liquid helium II came from extensive measurements of the phonon–roton and multiphonon parts of the inelastic scattering. After the first two decades, neutron experiments continued at Chalk River until the shut-down of the NRU reactor in 2018 and the disbanding of the neutron effort in 2019, seventy years after the first experiments.

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Section: Epiloguementioning

confidence: 89%

The First Two Decades of Neutron Scattering at the Chalk River Laboratories

Holden

2021

QuBS

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“…In experiments, the quest for a doubly superfluid Bose-Fermi of the mixture continues [15], despite extraordinary technical difficulties to reach its predicted critical temperature of about 45 µK [16]. Another challenge regarding 3 He atoms occurs in experiments with neutrons, where an absorption cross-section of about 10 4 barns [17] makes observations of the intensity of the scattered neutrons extremely difficult. On the theoretical side, a qualitative understanding of many characteristics of helium mixtures involves a delicate balance between several effects, including the local density, the Heisenberg uncertainty principle, an attraction between 3 He atoms due to magnetic interaction caused by nuclear magnetic moments, the Pauli exclusion principle, and atomic binding energies [18].…”

Section: Introductionmentioning

confidence: 99%

Properties of fermionic systems with the path-integral ground state method

et al. 2023

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We investigate strongly correlated many-body systems composed of bosons and fermions with a fully quantum treatment using the path-integral ground state method, PIGS. To account for the Fermi-Dirac statistics, we implement the fixed-node approximation into PIGS, which we then call FN-PIGS. In great detail, we discuss the pair density matrices we use to construct the full density operator in coordinate representation, a vital ingredient of the method. We consider the harmonic oscillator as a proof-of-concept and, as a platform representing quantum many-body systems, we explore helium atoms. Pure ^44He systems demonstrate most of the features of the method. Complementarily, for pure ^33He, the fixed-node approximation resolves the ubiquitous sign problem stemming from anti-symmetric wave functions. Finally, we investigate ^33He-^44He mixtures, demonstrating the method’s robustness. One of the main features of FN-PIGS is its ability to estimate any property at temperature T = 0T=0 without any additional bias apart from the FN approximation; biases from long simulations are also excluded. In particular, we calculate the correlation function of pairs of equal and opposite spins and precise values of the ^33He kinetic energy in the mixture.

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“…Another challenge regarding 3 He atoms occurs in experiments with neutrons, where an absorption cross-section of about 10 4 barns (Glyde, 2020) makes observations of the intensity of the scattered neutrons extremely difficult. On the theoretical side, a qualitative understanding of many characteristics of helium mixtures involves a delicate balance between several effects, including the local density, the Heisenberg uncertainty principle, an attraction between 3 He atoms due to magnetic interaction caused by nuclear magnetic moments, the Pauli exclusion principle, and atomic binding energies (Pobell, 2007).…”

Section: Introductionmentioning

confidence: 99%

Ground state properties of fermionic systems with the Density Matrix Projection method

Ujevick¹,

Zampronio²,

Abreu³

et al. 2022

Preprint

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We investigate several quantum many-body systems using the density matrix projection method. We consider a detailed proof of concept with the harmonic oscillator and apply the method to systems composed of fermions, bosons, and mixtures of bosons and fermions within the framework provided by Helium atoms. Bosons serve to demonstrate most of the features of the method. Complementarily, when considering systems described by anti-symmetrical wavefunctions, introducing the fixed-node approximation is the way we choose to avoid the ubiquitous sign problem. One of the main features of the method is its ability to estimate any property at temperature T = 0 without bias, including biases that come from long-running simulations. In great detail, we discuss pair density matrices that we use to construct the full density operator in coordinate representation. Finally, we investigate 3 He-4 He mixtures, showing the robustness of the density matrix projection method. In particular, we calculate the pair correlation function of equal and opposite spins and accurate values of the 3 He kinetic energy.

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Quantum liquids

Abstract: Roger did much of his PhD thesis research at CRNL in 1961-2, on structural transitions and anharmonic phonons in solids. After completing his doctorate at the University of Cambridge and his marriage to Sheila, Roger returned to CRNL as a staff

Cited by 3 publications

References 82 publications

The First Two Decades of Neutron Scattering at the Chalk River Laboratories

The First Two Decades of Neutron Scattering at the Chalk River Laboratories

Properties of fermionic systems with the path-integral ground state method

Ground state properties of fermionic systems with the Density Matrix Projection method

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