750 research outputs found
Teleportation of a quantum state of a spatial mode with a single massive particle
Mode entanglement exists naturally between regions of space in ultra-cold
atomic gases. It has, however, been debated whether this type of entanglement
is useful for quantum protocols. This is due to a particle number
superselection rule that restricts the operations that can be performed on the
modes. In this paper, we show how to exploit the mode entanglement of just a
single particle for the teleportation of an unknown quantum state of a spatial
mode. We detail how to overcome the superselection rule to create any initial
quantum state and how to perform Bell state analysis on two of the modes. We
show that two of the four Bell states can always be reliably distinguished,
while the other two have to be grouped together due to an unsatisfied phase
matching condition. The teleportation of an unknown state of a quantum mode
thus only succeeds half of the time.Comment: 12 pages, 1 figure, this paper was presented at TQC 2010 and extends
the work of Phys. Rev. Lett. 103, 200502 (2009
Performances and robustness of quantum teleportation with identical particles
When quantum teleportation is performed with truly identical massive
particles, indistinguishability allows us to teleport addressable degrees of
freedom which do not identify particles, but e.g. orthogonal modes. The key
resource of the protocol is a state of entangled modes, but the conservation of
the total number of particles does not allow for perfect deterministic
teleportation unless the number of particles in the resource state goes to
infinity. Here, we study the convergence of teleportation performances in the
above limit, and provide sufficient conditions for asymptotic perfect
teleporation. We also apply these conditions to the case of resource states
affected by noise
Quantum Entanglement and Teleportation in Higher Dimensional Black Hole Spacetimes
We study the properties of quantum entanglement and teleportation in the
background of stationary and rotating curved space-times with extra dimensions.
We show that a maximally entangled Bell state in an inertial frame becomes less
entangled in curved space due to the well-known Hawking-Unruh effect. The
degree of entanglement is found to be degraded with increasing the extra
dimensions. For a finite black hole surface gravity, the observer may choose
higher frequency mode to keep high level entanglement. The fidelity of quantum
teleporation is also reduced because of the Hawking-Unruh effect. We discuss
the fidelity as a function of extra dimensions, mode frequency, black hole mass
and black hole angular momentum parameter for both bosonic and fermionic
resources.Comment: 15 pages, 10 figures,contents expande
Photonic Entanglement for Fundamental Tests and Quantum Communication
Entanglement is at the heart of fundamental tests of quantum mechanics like
tests of Bell-inequalities and, as discovered lately, of quantum computation
and communication. Their technological advance made entangled photons play an
outstanding role in entanglement physics. We give a generalized concept of
qubit entanglement and review the state of the art of photonic experiments.Comment: 54 pages, 33 figures. Review article submitted to QIC (Rinton
Twisted Photons: New Quantum Perspectives in High Dimensions
Quantum information science and quantum information technology have seen a
virtual explosion world-wide. It is all based on the observation that
fundamental quantum phenomena on the individual particle or system-level lead
to completely novel ways of encoding, processing and transmitting information.
Quantum mechanics, a child of the first third of the 20th century, has found
numerous realizations and technical applications, much more than was thought at
the beginning. Decades later, it became possible to do experiments with
individual quantum particles and quantum systems. This was due to technological
progress, and for light in particular, the development of the laser. Hitherto,
nearly all experiments and also nearly all realizations in the fields have been
performed with qubits, which are two-level quantum systems. We suggest that
this limitation is again mainly a technological one, because it is very
difficult to create, manipulate and measure more complex quantum systems. Here,
we provide a specific overview of some recent developments with
higher-dimensional quantum systems. We mainly focus on Orbital Angular Momentum
(OAM) states of photons and possible applications in quantum information
protocols. Such states form discrete higher-dimensional quantum systems, also
called qudits. Specifically, we will first address the question what kind of
new fundamental properties exist and the quantum information applications which
are opened up by such novel systems. Then we give an overview of recent
developments in the field by discussing several notable experiments over the
past 2-3 years. Finally, we conclude with several important open questions
which will be interesting for investigations in the future.Comment: 15 pages, 7 figure
Observer dependent entanglement
Understanding the observer-dependent nature of quantum entanglement has been
a central question in relativistic quantum information. In this paper we will
review key results on relativistic entanglement in flat and curved spacetime
and discuss recent work which shows that motion and gravity have observable
effects on entanglement between localized systems.Comment: Ivette Fuentes previously published as Ivette Fuentes-Guridi and
Ivette Fuentes-Schulle
Spatially extended Unruh-DeWitt detectors for relativistic quantum information
Unruh-DeWitt detectors interacting locally with a quantum field are systems
under consideration for relativistic quantum information processing. In most
works, the detectors are assumed to be point-like and, therefore, couple with
the same strength to all modes of the field spectrum. We propose the use of a
more realistic detector model where the detector has a finite size conveniently
tailored by a spatial profile. We design a spatial profile such that the
detector, when inertial, naturally couples to a peaked distribution of
Minkowski modes. In the uniformly accelerated case, the detector couples to a
peaked distribution of Rindler modes. Such distributions are of special
interest in the analysis of entanglement in non-inetial frames. We use our
detector model to show the noise detected in the Minkowski vacuum and in single
particle states is a function of the detector's acceleration.Comment: Revised for publication, 9 pages (+1 references page), 7 figure
Localized qubits in curved spacetimes
We provide a systematic and self-contained exposition of the subject of
localized qubits in curved spacetimes. This research was motivated by a simple
experimental question: if we move a spatially localized qubit, initially in a
state |\psi_1>, along some spacetime path \Gamma from a spacetime point x_1 to
another point x_2, what will the final quantum state |\psi_2> be at point x_2?
This paper addresses this question for two physical realizations of the qubit:
spin of a massive fermion and polarization of a photon. Our starting point is
the Dirac and Maxwell equations that describe respectively the one-particle
states of localized massive fermions and photons. In the WKB limit we show how
one can isolate a two-dimensional quantum state which evolves unitarily along
\Gamma. The quantum states for these two realizations are represented by a
left-handed 2-spinor in the case of massive fermions and a four-component
complex polarization vector in the case of photons. In addition we show how to
obtain from this WKB approach a fully general relativistic description of
gravitationally induced phases. We use this formalism to describe the
gravitational shift in the COW 1975 experiment. In the non-relativistic weak
field limit our result reduces to the standard formula in the original paper.
We provide a concrete physical model for a Stern-Gerlach measurement of spin
and obtain a unique spin operator which can be determined given the orientation
and velocity of the Stern-Gerlach device and velocity of the massive fermion.
Finally, we consider multipartite states and generalize the formalism to
incorporate basic elements from quantum information theory such as quantum
entanglement, quantum teleportation, and identical particles. The resulting
formalism provides a basis for exploring precision quantum measurements of the
gravitational field using techniques from quantum information theory.Comment: 53 pages, 7 figures; v2: published version with further corrections.
v3: some references and equation typesetting fixe
- …