Search results for "Quantum phases"
showing 9 items of 19 documents
Appearance of Fermion-Condensation Quantum Phase Transition in Fermi Systems
2014
As high-\(T_c\) superconductors are represented primarily by 2D layered structures, in Sect. 5.1 we discuss the superconducting state of a 2D liquid of heavy electrons, and within the framework of Gor’kov microscopic equations construct the Green functions of the FC state. On the other hand, our study can easily be generalized to the 3D case. To show that there is no fundamental difference between the 2D and 3D cases, we derive Green’s functions for the 3D case in Sect. 5.1.1. In Sect. 5.2, we consider the dispersion law and lineshape of single-particle excitations. Section 5.3 is devoted to the behavior of heavy-electron liquid with FC in magnetic field. In Sect. 5.4, we analyze conditions…
From where do quantum groups come?
1993
The phase space realizations of quantum groups are discussed using *-products. We show that on phase space, quantum groups appear necessarily as two-parameter deformation structures, one parameter (v) being concerned with the quantization in phase space, the other (η) expressing the quantum groups as “deformation” of their Lie counterparts. Introducing a strong invariance condition, we show the uniqueness of the η-deformation. This suggests that the strong invariance condition is a possible origin of the quantum groups.
Phase transition of light on complex quantum networks
2012
Recent advances in quantum optics and atomic physics allow for an unprecedented level of control over light-matter interactions, which can be exploited to investigate new physical phenomena. In this work we are interested in the role played by the topology of quantum networks describing coupled optical cavities and local atomic degrees of freedom. In particular, using a mean-field approximation, we study the phase diagram of the Jaynes-Cummings-Hubbard model on complex networks topologies, and we characterize the transition between a Mott-like phase of localized polaritons and a superfluid phase. We found that, for complex topologies, the phase diagram is non-trivial and well defined in the…
The influence of quantum fluctuations on phase transition temperature in disordered ferroelectrics
2014
We consider the disordered ferroelectric, where the impurity dipoles interact via quantum optical phonons. We show that quantum fluctuations are amplified by the effects of disorder so that they can be important up to the ferroelectric phase transition temperature. In this paper, we calculate the ferroelectric phase transition temperature as a function of impurity dipole concentration. We show that quantum effects change the character of concentrational dependence of . Namely, they cause the discontinuity in so that the critical concentration is reached abruptly. We have shown that quantum effects inhibit the ferroelectricity so that larger (than that in purely classical disordered ferroele…
Ordering phenomena and phase transitions in the physisorbed quantum systems H2, HD and D2
1991
Abstract Recent experimental results of H2, HD and D2 films physisorbed on graphite are briefly reviewed. In particular, the monolayer phase diagrams, the order-disorder transition of the commensurate (C) phase and the commensurate-incommensurate (C-IC) transition are discussed. It will be shown that the melting transition of the C phase belongs to the three-state Potts universality class, and that the C-IC transition occurs via a series of novel intermediate phase, which could be identified as density-modulated phases characterized by striped and hexagonal patterns of domain walls. Due to this rich variety of phenomena, the hydrogen isotopes can be considered as model systems for two-dimen…
Quantum fluctuations and coherence in high-precision single-electron capture.
2012
The phase of a single quantum state is undefined unless the history of its creation provides a reference point. Thus quantum interference may seem hardly relevant for the design of deterministic single-electron sources which strive to isolate individual charge carriers quickly and completely. We provide a counterexample by analyzing the non-adiabatic separation of a localized quantum state from a Fermi sea due to a closing tunnel barrier. We identify the relevant energy scales and suggest ways to separate the contributions of quantum non-adiabatic excitation and backtunneling to the rare non-capture events. In the optimal regime of balanced decay and non-adiabaticity, our simple electron tr…
Symmetry-protected intermediate trivial phases in quantum spin chains
2015
Symmetry-protected trivial (SPt) phases of matter are the product-state analogue of symmetry-protected topological (SPT) phases. This means, SPt phases can be adiabatically connected to a product state by some path that preserves the protecting symmetry. Moreover, SPt and SPT phases can be adiabatically connected to each other when interaction terms that break the symmetries protecting the SPT order are added in the Hamiltonian. It is also known that spin-1 SPT phases in quantum spin chains can emerge as effective intermediate phases of spin-2 Hamiltonians. In this paper we show that a similar scenario is also valid for SPt phases. More precisely, we show that for a given spin-2 quantum cha…
Observability of the sign of wave functions
1976
A change of the phase factor of -1 in the wave function of a molecular quantum system leads to observable consequences in transition probabilities between molecular quantum states in accordance with quantum-mechanical calculations.
Small clusters with anisotropic antiferromagnetic exchange in a magnetic field
2004
We consider small symmetric clusters of magnetic atoms (spins) with anisotropic exchange interaction between the atoms in a magnetic field at zero temperature. The inclusion of the anisotropy leads to a wealth of different phases as a function of the applied magnetic field. These are not phases in the thermodynamic sense with critical properties but rather physical structures with different arrangements of the spins and hence different symmetries. We study the spatial symmetry of these phases, for the classical and quantum cases. Results are presented mainly for three frustrated systems, the triangle, the tetrahedron and the five-atom ring, which have many interesting features. In the class…