566 research outputs found
Dynamics of quantum correlations and linear entropy in a multi-qubit-cavity system
We present a theoretical study of the relationship between entanglement and
entropy in multi-qubit quantum optical systems. Specifically we investigate
quantitative relations between the concurrence and linear entropy for a
two-qubit mixed system, implemented as two two-level atoms interacting with a
single-mode cavity field. The dynamical evolutions of the entanglement and
entropy, are controlled via time-dependent cavity-atom couplings. Our
theoretical findings lead us to propose an alternative measure of entanglement,
which could be used to develop a much needed correlation measure for more
general multi-partite quantum systems.Comment: New discussions on the generality of entanglement-entropy
relationship, one new reference, and other minor changes. 10 pages, 6
figures, accepted for publication in J.Opt. B: "Special Issue on Fluctuations
& Noise in Photonics & Quantum Optics.
Generation of three-qubit entangled states using coupled multi-quantum dots
We discuss a mechanism for generating a maximum entangled state (GHZ) in a
coupled quantum dots system, based on analytical techniques. The reliable
generation of such states is crucial for implementing solid-state based quantum
information schemes. The signature originates from a remarkably weak field
pulse or a far off-resonance effects which could be implemented using
technology that is currently being developed. The results are illustrated with
an application to a specific wide-gap semiconductor quantum dots system, like
Zinc Selenide (ZnSe) based quantum dots.Comment: 8 pages, 2 figure
Transient synchronisation and quantum coherence in a bio-inspired vibronic dimer
Synchronisation is a collective phenomenon widely investigated in classical oscillators and, more recently, in quantum systems. However it remains unclear what features distinguish synchronous behaviour in these two scenarios. Recent works have shown that investigating synchronisation dynamics in open quantum systems can give insight into this issue. Here we study transient synchronisation in a bio-inspired vibronic dimer, where electronic excitation dynamics is mediated by coherent interactions with intramolecular vibrational modes. We show that the synchronisation dynamics of local mode displacements exhibit a rich behaviour which arises directly from the distinct time-evolutions of different vibronic quantum coherences. Furthermore, our study shows that coherent energy transport in this bio-inspired system is concomitant with the emergence of positive synchronisation between mode displacements. Our work provides further understanding of the relations between quantum coherence and synchronisation in open quantum systems and suggests an interesting role for coherence in biomolecules, that of promoting synchronisation of vibrational motions driven out of thermal equilibrium
Energy resolution of terahertz single-photon-sensitive bolometric detectors
We report measurements of the energy resolution of ultra-sensitive
superconducting bolometric detectors. The device is a superconducting titanium
nanobridge with niobium contacts. A fast microwave pulse is used to simulate a
single higher-frequency photon, where the absorbed energy of the pulse is equal
to the photon energy. This technique allows precise calibration of the input
coupling and avoids problems with unwanted background photons. Present devices
have an intrinsic full-width at half-maximum energy resolution of approximately
23 terahertz, near the predicted value due to intrinsic thermal fluctuation
noise.Comment: 11 pages (double-spaced), 5 figures; minor revision
Maximally entangled mixed states of two atoms trapped inside an optical cavity
In some off-resonant cases, the reduced density matrix of two atoms
symmetrically coupled with an optical cavity can very approximately approach to
maximally entangled mixed states or maximal Bell violation mixed states in
their evolution. The influence of phase decoherence on the generation of
maximally entangled mixed state is also discussed.
PACS numbers: 03.67.-a, 03.65.UdComment: 7 pages, 4 figures, Latex, have a major revision of content
Optical signatures of quantum phase transitions in a light-matter system
Information about quantum phase transitions in conventional condensed matter
systems, must be sought by probing the matter system itself. By contrast, we
show that mixed matter-light systems offer a distinct advantage in that the
photon field carries clear signatures of the associated quantum critical
phenomena. Having derived an accurate, size-consistent Hamiltonian for the
photonic field in the well-known Dicke model, we predict striking behavior of
the optical squeezing and photon statistics near the phase transition. The
corresponding dynamics resemble those of a degenerate parametric amplifier. Our
findings boost the motivation for exploring exotic quantum phase transition
phenomena in atom-cavity, nanostructure-cavity, and
nanostructure-photonic-band-gap systems.Comment: 4 pages, 4 figure
Quantitative aspects of entanglement in the optically driven quantum dots
We present a novel approach to look for the existence of maximum entanglement
in a system of two identical quantum dots coupled by the Forster process and
interacting with a classical laser field. Our approach is not only able to
explain the existing treatments, but also provides further detailed insights
into the coupled dynamics of quantum dots systems. The result demonstrates that
there are two ways for generating maximum entangled states, one associated with
far off-resonance interaction, and the other associated with the weak field
limit. Moreover, it is shown that exciton decoherence results in the decay of
entanglement.Comment: 13 pages, 4 figure
- …