418 research outputs found
Relativistic entanglement in single-particle quantum states using Non-Linear entanglement witnesses
In this study, the spin-momentum correlation of one massive spin-1/2 and
spin-1 particle states, which are made based on projection of a relativistic
spin operator into timelike direction is investigated. It is shown that by
using Non-Linear entanglement witnesses (NLEWs), the effect of Lorentz
transformation would decrease both the amount and the region of entanglement.Comment: 16 pages, 2 figures; to be published in Quantum Inf Process,
10.1007/s11128-011-0289-z (2011
Quantum gates and multipartite entanglement resonances realized by non-uniform cavity motion
We demonstrate the presence of genuine multipartite entanglement between the
modes of quantum fields in non-uniformly moving cavities. The transformations
generated by the cavity motion can be considered as multipartite quantum gates.
We present two setups for which multi-mode entanglement can be generated for
bosons and fermions. As a highlight we show that the bosonic genuine
multipartite correlations can be resonantly enhanced. Our results provide
fundamental insights into the structure of Bogoliubov transformations and
suggest strong links between quantum information, quantum fields in curved
spacetimes and gravitational analogs by way of the equivalence principle.Comment: v2: extended to 9 pages, 2 figures, appendix with explicit witness
inequalities added; to appear in Phys. Rev. D; Ivette Fuentes previously
published as Ivette Fuentes-Guridi and Ivette Fuentes-Schulle
Entanglement between smeared field operators in the Klein-Gordon vacuum
Quantum field theory is the application of quantum physics to fields. It
provides a theoretical framework widely used in particle physics and condensed
matter physics. One of the most distinct features of quantum physics with
respect to classical physics is entanglement or the existence of strong
correlations between subsystems that can even be spacelike separated. In
quantum fields, observables restricted to a region of space define a subsystem.
While there are proofs on the existence of local observables that would allow a
violation of Bell's inequalities in the vacuum states of quantum fields as well
as some explicit but technically demanding schemes requiring an extreme
fine-tuning of the interaction between the fields and detectors, an
experimentally accessible entanglement witness for quantum fields is still
missing. Here we introduce smeared field operators which allow reducing the
vacuum to a system of two effective bosonic modes. The introduction of such
collective observables is motivated by the fact that no physical probe has
access to fields in single spatial (mathematical) points but rather smeared
over finite volumes. We first give explicit collective observables whose
correlations reveal vacuum entanglement in the Klein-Gordon field. We then show
that the critical distance between the two regions of space above which two
effective bosonic modes become separable is of the order of the Compton
wavelength of the particle corresponding to the massive Klein-Gordon field.Comment: 21 pages, 11 figure
On Bell's theorem, quantum communication, and entanglement detection
(A) Bell's theorem rests on a conjunction of three assumptions: realism,
locality and ``free will''. A discussion of these assumptions will be
presented.
It will be also shown that, if one adds to the assumptions the principle or
rotational symmetry of physical laws, a stronger version of the theorem
emerges. (B) A link between Bell's theorem and communication complexity
problems will be presented. This also includes experimental realizations, which
surprisingly do not involve entanglement. (C) A new sufficient and necessary
criterion for entanglement of general (mixed) states is be presented. It is
derived using the same geometric starting point as the inclusion of the
symmetry in (A). The set of entanglement identifiers (EI's) emerging via this
method contains entanglement witnesses (EW's), but they form only a subset of
all EI's. Thus the method is more powerful than the one based on EW's.Comment: 10 pages, for proceedings of Foundations of Probability and Physics-5
at Vaxjo University, Swedish Southeast Academy August 24-27, 200
Relativistic entanglement of two massive particles
We describe the spin and momentum degrees of freedom of a system of two
massive spin-- particles as a 4 qubit system. Then we explicitly
show how the entanglement changes between different partitions of the qubits,
when considered by different inertial observers. Although the two particle
entanglement corresponding to a partition into Alice's and Bob's subsystems is,
as often stated in the literature, invariant under Lorentz boosts, the
entanglement with respect to other partitions of the Hilbert space on the other
hand, is not. It certainly does depend on the chosen inertial frame and on the
initial state considered. The change of entanglement arises, because a Lorentz
boost on the momenta of the particles causes a Wigner rotation of the spin,
which in certain cases entangles the spin- with the momentum states. We
systematically investigate the situation for different classes of initial spin
states and different partitions of the 4 qubit space.
Furthermore, we study the behavior of Bell inequalities for different
observers and demonstrate how the maximally possible degree of violation, using
the Pauli-Lubanski spin observable, can be recovered by any inertial observer.Comment: 17 pages, 4 figure
Orbital angular momentum of photons and the entanglement of Laguerre-Gaussian modes
The identification of orbital angular momentum (OAM) as a fundamental
property of a beam of light nearly twenty-five years ago has led to an
extensive body of research around this topic. The possibility that single
photons can carry OAM has made this degree of freedom an ideal candidate for
the investigation of complex quantum phenomena and their applications. Research
in this direction has ranged from experiments on complex forms of quantum
entanglement to the interaction between light and quantum states of matter.
Furthermore, the use of OAM in quantum information has generated a lot of
excitement, as it allows for encoding large amounts of information on a single
photon. Here we explain the intuition that led to the first quantum experiment
with OAM fifteen years ago. We continue by reviewing some key experiments
investigating fundamental questions on photonic OAM and the first steps into
applying these properties in novel quantum protocols. In the end, we identify
several interesting open questions that could form the subject of future
investigations with OAM.Comment: 17 pages, 7 figures; close to accepted versio
- …