Nguyen Thanh Phuc
University of Tokyo
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Featured researches published by Nguyen Thanh Phuc.
Nature Communications | 2015
Nguyen Thanh Phuc; Gen Tatara; Yuki Kawaguchi; Masahito Ueda
Gauge fields, typified by the electromagnetic field, often appear as emergent phenomena due to geometrical properties of a curved Hilbert subspace, and provide a key mechanism for understanding such exotic phenomena as the anomalous and topological Hall effects. Non-abelian gauge potentials serve as a source of non-singular magnetic monopoles. Here we show that unlike conventional solid materials, the non-abelianness of emergent gauge potentials in spinor Bose-Fermi atomic mixtures can be continuously varied by changing the relative particle-number densities of bosons and fermions. The non-abelian feature is captured by an explicit dependence of the measurable spin current density of fermions in the mixture on the variable coupling constant. Spinor mixtures also provide us with a method to coherently and spontaneously generate a pure spin current without relying on the spin Hall effect. Such a spin current is expected to have potential applications in the new generation of atomtronic devices.
Physical Review Letters | 2014
Nguyen Thanh Phuc; Yuki Kawaguchi; Masahito Ueda
Quantum mass acquisition, in which a massless (quasi)particle becomes massive due to quantum corrections, is predicted to occur in several subfields of physics. However, its experimental observation remains elusive since the emergent energy gap is too small. We show that a spinor Bose-Einstein condensate is an excellent candidate for the observation of such a peculiar phenomenon as the energy gap turns out to be 2 orders of magnitude larger than the zero-point energy. This extraordinarily large energy gap is a consequence of the dynamical instability. The propagation velocity of the resultant massive excitation mode is found to be decreased by the quantum corrections as opposed to phonons.
Physical Review A | 2013
Nguyen Thanh Phuc; Yuki Kawaguchi; Masahito Ueda
Spinor Bose-Einstein condensates provide a unique example in which the Bogoliubov theory fails to describe the metastability associated with first-order quantum phase transitions. This problem is resolved by developing the spinor Beliaev theory which takes account of quantum fluctuations of the condensate. It is these fluctuations that generate terms of higher than the fourth order in the order-parameter field which are needed for the first-order phase transitions. Besides the conventional first-order phase transitions which are accompanied by metastable states, we find a class of first-order phase transitions which are not accompanied by metastable states. The absence of metastability in these phase transitions holds to all orders of approximation since the metastability is prohibited by the symmetry of the Hamiltonian at the phase boundary. Finally, the possibility of macroscopic quantum tunneling from a metastable state to the ground state is discussed.
Physical Review A | 2012
Yuki Kawaguchi; Nguyen Thanh Phuc; P. Blair Blakie
We formulate a self-consistent Hartree-Fock theory for a spin-1 Bose gas at finite temperature and apply it to characterization of the phase diagram. We find that spin coherence between thermal atoms in different magnetic sublevels develops via coherent collisions with the condensed atoms, and is a crucial factor in determining the phase diagram. We develop analytical expressions to characterize the interaction- and temperature-dependent shifts of the phase boundaries.
Journal of Physical Chemistry Letters | 2018
Nguyen Thanh Phuc; Akihito Ishizaki
Excitation energy transfer (EET) is one of the most important processes in both natural and artificial chemical systems including, for example, photosynthetic complexes and organic solar cells. The EET rate, however, is strongly suppressed when there is a large difference in the excitation energy between the donor and acceptor molecules. Here, we demonstrate both analytically and numerically that the EET rate can be greatly enhanced by periodically modulating the excitation energy difference. The enhancement of EET by using this Floquet engineering, in which the systems Hamiltonian is made periodically time-dependent, turns out to be efficient even in the presence of strong fluctuations and dissipations induced by the coupling with a huge number of dynamic degrees of freedom in the surrounding molecular environments. As an effect of the environment on the Floquet engineering of EET, the optimal driving frequency is found to depend on the relative magnitudes of the system and environments characteristic time scales with an observed frequency shift when moving from the limit of slow environmental fluctuations (inhomogeneous broadening limit) to that of fast fluctuations (homogeneous broadening limit).
Physical Review A | 2017
Nguyen Thanh Phuc; Tsutomu Momoi; Shunsuke Furukawa; Yuki Kawaguchi; Takeshi Fukuhara; Masahito Ueda
Coarsening dynamics theory has successfully described the equilibration of a broad class of this http URL studying the relaxation of a periodic array of microcondensates immersed in a Fermi gas which can mediate long-range spin interactions to simulate frustrated classical magnets, we show that coarsening dynamics can be suppressed by geometrical frustration. The system is found to eventually approach a metastable state which is robust against random field noise and characterized by finite correlation lengths with the emergence of topologically stable Z2 vortices. We find universal scaling laws with no thermal-equilibrium analog that relate the correlation lengths and the number of vortices to the degree of frustration in the system.
Physical Review A | 2011
Nguyen Thanh Phuc; Yuki Kawaguchi
Annals of Physics | 2013
Nguyen Thanh Phuc; Yuki Kawaguchi; Masahito Ueda
arXiv: Mesoscale and Nanoscale Physics | 2018
Nguyen Thanh Phuc; Akihito Ishizaki
Physical Review A | 2018
Nguyen Thanh Phuc; Masahito Ueda