26 research outputs found
Quantum teleportation with squeezed vacuum states
We show how the partial entanglement inherent in a two mode squeezed vacuum
state admits two different teleportation protocols. These two protocols refer
to the different kinds of joint measurements that may be made by the sender.
One protocol is the recently implemented quadrature phase approach of
Braunstein and Kimble[Phys. Rev. Lett.{\bf 80}, 869 (1998)]. The other is based
on recognising that a two mode squeezed vacuum state is also entangled with
respect to photon number difference and phase sum. We show that this protocol
can also realise teleportation, however limitations can arise due to the fact
that the photon number spectrum is bounded from below by zero. Our examples
show that a given entanglement resource may admit more than a single
teleportation protocol and the question then arises as to what is the optimum
protocol in the general case
A Measure of Stregth of an Unextendible Product Basis
A notion of strength of an unextendible product basis is introduced and a
quantitative measure for it is suggested with a view to providing an indirect
measure for the bound entanglement of formation of the bound entangled mixed
state associated with an unextendible product basis.Comment: 4 pages, Latex, 1 figure, remarks, criticisms welcom
Quantum cryptography with squeezed states
A quantum key distribution scheme based on the use of displaced squeezed
vacuum states is presented. The states are squeezed in one of two field
quadrature components, and the value of the squeezed component is used to
encode a character from an alphabet. The uncertainty relation between
quadrature components prevents an eavesdropper from determining both with
enough precision to determine the character being sent. Losses degrade the
performance of this scheme, but it is possible to use phase-sensitive
amplifiers to boost the signal and partially compensate for their effect.Comment: 15 pages, no figure
Universal teleportation with a twist
We give a transfer theorem for teleportation based on twisting the
entanglement measurement. This allows one to say what local unitary operation
must be performed to complete the teleportation in any situation, generalizing
the scheme to include overcomplete measurements, non-abelian groups of local
unitary operations (e.g., angular momentum teleportation), and the effect of
non-maximally entangled resources.Comment: 4 pages, 1 figur
Detection of entanglement with few local measurements
We introduce a general method for the experimental detection of entanglement
by performing only few local measurements, assuming some prior knowledge of the
density matrix. The idea is based on the minimal decomposition of witness
operators into a pseudo-mixture of local operators. We discuss an
experimentally relevant case of two qubits, and show an example how bound
entanglement can be detected with few local measurements.Comment: 5 pages + 1 figur
Canonical Quantum Teleportation
Canonically conjugated observables such as position-momentum and phase-number
are found to play a 3-fold role in the drama of the quantum teleportation.
Firstly, the common eigenstate of two commuting canonical observables like
phase-difference and number-sum provides the quantum channel between two
systems. Secondly, a similar pair of canonical observables from another two
systems is measured in the Bell operator measurements.Comment: revtex,4 pages,e-mail:[email protected] www.itp.ac.cn/~suncp; The
Institute of Theoretical Physics, Academia Sinica, Beijing 100080, P.R. Chin
Soliton Squeezing in a Mach-Zehnder Fiber Interferometer
A new scheme for generating amplitude squeezed light by means of soliton
self-phase modulation is experimentally demonstrated. By injecting 180-fs
pulses into an equivalent Mach-Zehnder fiber interferometer, a maximum noise
reduction of dB is obtained ( dB when corrected for
losses). The dependence of noise reduction on the interferometer splitting
ratio and fiber length is studied in detail.Comment: 5 pages, 4 figure
Weak force detection with superposed coherent states
We investigate the utility of non classical states of simple harmonic
oscillators, particularly a superposition of coherent states, for sensitive
force detection. We find that like squeezed states a superposition of coherent
states allows displacement measurements at the Heisenberg limit. Entangling
many superpositions of coherent states offers a significant advantage over a
single mode superposition states with the same mean photon number.Comment: 6 pages, no figures: New section added on entangled resources.
Changes to discussions and conclusio
Quantitative wave-particle duality and non-erasing quantum erasure
The notion of wave-particle duality may be quantified by the inequality
V^2+K^2 <=1, relating interference fringe visibility V and path knowledge K.
With a single-photon interferometer in which polarization is used to label the
paths, we have investigated the relation for various situations, including
pure, mixed, and partially-mixed input states. A quantum eraser scheme has been
realized that recovers interference fringes even when no which-way information
is available to erase.Comment: 6 pages, 4 figures. To appear in Phys. Rev.