Beats and expansion of two-component Bose-Einstein condensates in the Thomas-Fermi limit

Published 23 October 2014A unique feature of multi-component Bose–Einstein condensates (BECs) is the possibility of beating frequencies in collective oscillations. We analytically determine this beating frequency for the two-component BEC in one-dimension. We also show that the Thomas–Fermi approximation, where the quantum pressure is neglected, describes well the expansion of the two-component condensate released from an harmonic trap.James Q Quac

Foldy-Wouthuysen transformation of the generalized Dirac Hamiltonian in a gravitational-wave background

Published 21 October 2015Goncalves et al. [Phys. Rev. D 75, 124023 (2007)] derived a nonrelativistic limit of the generalized Dirac Hamiltonian in the presence of a gravitational wave, using the exact Foldy-Wouthuysen transformation. This gave rise to the intriguing notion that spin precession may occur even in the absence of a magnetic field. We argue that this effect is not physical as it is the result of a gauge-variant term that was an artifact of a flawed application of the exact Foldy-Wouthuysen transformation. In this paper we derive the correct nonrelativistic limit of the generalized Dirac Hamiltonian in the presence of a gravitational wave, using both the exact and standard Foldy-Wouthuysen transformation. We show that both transformations consistently produce a Hamiltonian where all terms are gauge invariant. Unfortunately however, we also show that this means the novel spin-precession effect does not exist.James Q. Quac

Which-way double-slit experiments and Born-rule violation

Published 24 April 2017In which-way double-slit experiments with perfect detectors, it is assumed that having a second detector at the slits is redundant because it will not change the interference pattern. We, however, show that if higher-order or nonclassical paths are accounted for, the presence of the second detector will have an effect on the interference pattern. Accounting for these nonclassical paths also means that the Sorkin parameter in triple-slit experiments is only an approximate measure of Born-rule violation. Using the difference between single and double which-way detectors, we give an alternative parameter which is an exact measure of Born-rule violation.James Q. Quac

Experimental and computational characterisation of an artificial light harvesting complex

OnlinePublPhotosynthesis has been shown to be a highly efficient process for energy transfer in plants and bacteria. Like natural photosynthetic systems, the artificial light harvesting complex (LHC) BODIPY pillar[5]arene exhibits Fo¨rster resonance energy transfer (FRET). However, extensive characterisation of the BODIPY pillar[5]arene LHC to determine its suitability as an artificial LHC has yet to occur. In this paper we experimentally and computationally investigate the photophysical properties of the LHC by comparing the light absorption of the BODIPY LHC to individual BODIPY chromophores. Our results show evidence for quantum coherence, with oscillation frequencies of 100 cm1 and 600 cm1 , which are attributable to vibronic, or exciton–phonon type coupling. Computational analysis suggests strong couplings of the molecular orbitals of the LHC resulting from the stacking of neighbouring BODIPY chromophore units. Interestingly, we find a 40% reduction in the absorbance of light for the BODIPY LHC compared to the individual chromophores which we attribute to electronic interactions between the conjugated p-systems of the BODIPY chromophores and the pillar[5]arene backbone.Sabrina L. Slimani, Roman Kostecki, Ahmed Nuri Kursunlu, Tak W. Kee, Patrick C. Tapping, Adrian M. Mak and James Q. Quac

Quasi-superradiant soliton state of matter in quantum metamaterials

The final publication is available at Springer via https://doi.org/10.1140/epjb/e2017-80567-7Strong interaction of a system of quantum emitters (e.g., two-level atoms) with electromagnetic field induces specific correlations in the system accompanied by a drastic increase of emitted radiation (superradiation or superuorescence). Despite the fact that since its prediction this phenomenon was subject to a vigorous experimental and theoretical research, there remain open question, in particular, concerning the possibility of a first order phase transition to the superradiant state from the vacuum state. In systems of natural and charge-based artificial atom this transition is prohibited by \no-go" theorems. Here we demonstrate numerically and confirm analytically a similar transition in a one-dimensional quantum metamaterial { a chain of artificial atoms (qubits) strongly interacting with classical electromagnetic fields in a transmission line. The system switches from vacuum state to the quasi-superradiant (QS) phase with one or several magnetic solitons and finite average occupation of qubit excited states along the transmission line. A quantum metamaterial in the QS phase circumvents the \no-go" restrictions by considerably decreasing its total energy relative to the vacuum state by exciting nonlinear electromagnetic solitons