40 research outputs found
Temperature-controlled entangled-photon absorption spectroscopy
Entangled two-photon absorption spectroscopy (TPA) has been widely recognized as a powerful tool for revealing relevant information about the structure of complex molecular systems. However, to date, the experimental implementation of this technique has remained elusive, mainly because of two major difficulties: first, the need to perform multiple experiments with two-photon states bearing different temporal correlations, which translates into the necessity to have at the experimenter’s disposal tens, if not hundreds, of sources of entangled photons; second, the need to have a priori knowledge of the absorbing medium’s lowest-lying intermediate energy level. In this work, we put forward a simple experimental scheme that successfully overcomes these two limitations. By making use of a temperature-controlled entangled-photon source, which allows the tuning of the central frequencies of the absorbed photons, we show that the TPA signal, measured as a function of the temperature of the nonlinear crystal that generates the paired photons, and a controllable delay between them, carries all information about the electronic level structure of the absorbing medium, which can be revealed by a simple Fourier transformation.Peer ReviewedPostprint (author's final draft
Two-particle quantum correlations in stochastically-coupled networks
Quantum walks in dynamically-disordered networks have become an invaluable
tool for understanding the physics of open quantum systems. In this work, we
introduce a novel approach to describe the dynamics of indistinguishable
particles in noisy quantum networks. By making use of stochastic calculus, we
derive a master equation for the propagation of two non-interacting correlated
particles in tight-binding networks affected by off-diagonal dynamical
disorder. We show that the presence of noise in the couplings of a quantum
network creates a pure-dephasing-like process that destroys all coherences in
the single-particle Hilbert subspace. Remarkably, we find that when two or more
correlated particles propagate in the network, coherences accounting for
particle indistinguishability are robust against the impact of noise, thus
showing that it is possible, in principle, to find specific conditions for
which many indistinguishable particles can traverse dynamically-disordered
systems without losing their ability to interfere. These results shed light on
the role of particle indistinguishability in the preservation of quantum
coherence in dynamically-disordered quantum networks.Comment: 15 pages, 4 figure
Endurance of quantum coherence due to particle indistinguishability in noisy quantum networks
Quantum coherence, the physical property underlying fundamental phenomena
such as multi-particle interference and entanglement, has emerged as a valuable
resource upon which modern technologies are founded. In general, the most
prominent adversary of quantum coherence is noise arising from the interaction
of the associated dynamical system with its environment. Under certain
conditions, however, the existence of noise may drive quantum and classical
systems to endure intriguing nontrivial effects. In this vein, here we
demonstrate, both theoretically and experimentally, that when two
indistinguishable non-interacting particles co-propagate through quantum
networks affected by non-dissipative noise, the system always evolves into a
steady state in which coherences accounting for particle indistinguishabilty
perpetually prevail. Furthermore, we show that the same steady state with
surviving quantum coherences is reached even when the initial state exhibits
classical correlations.Comment: arXiv admin note: substantial text overlap with arXiv:1709.0433
Generating high-order exceptional points in coupled electronic oscillators using complex synthetic gauge fields
Exceptional points (EPs) are degeneracies of non-Hermitian systems, where
both eigenvalues and eigenvectors coalesce. Classical and quantum systems
exhibiting high-order EPs have recently been identified as fundamental building
blocks for the development of novel, ultra-sensitive opto-electronic devices.
However, arguably one of their major drawbacks is that they rely on non-linear
amplification processes that could limit their potential applications,
particularly in the quantum realm. In this work, we show that high-order EPs
can be designed by means of linear, time-modulated, chain of inductively
coupled RLC (where R stands for resistance, L for inductance, and C for
capacitance) electronic circuits. With a general theory, we show that
coupled circuits with dynamical variables and time-dependent parameters
can be mapped onto an -site, time-dependent, non-Hermitian Hamiltonian, and
obtain constraints for -symmetry in such models. With numerical
calculations, we obtain the Floquet exceptional contours of order by
studying the energy dynamics in the circuit. Our results pave the way toward
realizing robust, arbitrary-order EPs by means of synthetic gauge fields, with
important implications for sensing, energy transfer, and topology