26 research outputs found
Practical measurement of joint weak values and their connection to the annihilation operator
Weak measurements are a new tool for characterizing post-selected quantum
systems during their evolution. Weak measurement was originally formulated in
terms of von Neumann interactions which are practically available for only the
simplest single-particle observables. In the present work, we extend and
greatly simplify a recent, experimentally feasible, reformulation of weak
measurement for multiparticle observables [Resch and Steinberg (2004, Phys.
Rev. Lett., 92, 130402)]. We also show that the resulting ``joint weak values''
take on a particularly elegant form when expressed in terms of annihilation
operators.Comment: 13 pages, accepted to Physics Letters A (Dec. 2004
Experimental Realization of the Quantum Box Problem
The three-box problem is a gedankenexperiment designed to elucidate some
interesting features of quantum measurement and locality. A particle is
prepared in a particular superposition of three boxes, and later found in a
different (but nonorthogonal) superposition. It was predicted that appropriate
"weak" measurements of particle position in the interval between preparation
and post-selection would find the particle in two different places, each with
certainty. We verify these predictions in an optical experiment and address the
issues of locality and of negative probability.Comment: 5 pages, 4 figure
Non-deterministic Gates for Photonic Single Rail Quantum Logic
We discuss techniques for producing, manipulating and measureing qubits
encoded optically as vacuum and single photon states. We show that a universal
set of non-deterministic gates can be constructed using linear optics and
photon counting. We investigate the efficacy of a test gate given realistic
detector efficiencies.Comment: 8 pages, 6 figure
Entanglement and four wave mixing effects in the dissipation free nonlinear interaction of two photons at a single atom
We investigate the nonlinear interaction between two photons in a single
input pulse at an atomic two level nonlinearity. A one dimensional model for
the propagation of light to and from the atom is used to describe the precise
spatiotemporal coherence of the two photon state. It is shown that the
interaction generates spatiotemporal entanglement in the output state similar
to the entanglement observed in parametric downconversion. A method of
generating photon pairs from coherent pump light using this quantum mechanical
four wave mixing process is proposed.Comment: 10 pages, including 3 figures, correction in eq.(7), updated
references, final version for publication in PR
Observation of correlated-photon statistics using a single detector
We report experimental observations of correlated-photon statistics in the
single-photon detection rate. The usual quantum interference in a two-photon
polarization interferometer always accompanies a dip in the single detector
counting rate, regardless of whether a dip or peak is seen in the coincidence
rate. This effect is explained by taking into account all possible photon
number states that reach the detector, rather than considering just the state
post-selected by the coincidence measurement. We also report an
interferometeric scheme in which the interference peak or dip in coincidence
corresponds directly to a peak or dip in the single-photon detection rate.Comment: 4 pages, two-column (minor errors corrected.
Experimental Controlled-NOT Logic Gate for Single Photons in the Coincidence Basis
We report a proof-of-principle demonstration of a probabilistic
controlled-NOT gate for single photons. Single-photon control and target qubits
were mixed with a single ancilla photon in a device constructed using only
linear optical elements. The successful operation of the controlled-NOT gate
relied on post-selected three-photon interference effects which required the
detection of the photons in the output modes.Comment: 4 pages, 4 figures; minor change
Single Atom and Two Atom Ramsey Interferometry with Quantized Fields
Implications of field quantization on Ramsey interferometry are discussed and
general conditions for the occurrence of interference are obtained.
Interferences do not occur if the fields in two Ramsey zones have precise
number of photons. However in this case we show how two atom (like two photon)
interferometry can be used to discern a variety of interference effects as the
two independent Ramsey zones get entangled by the passage of first atom.
Generation of various entangled states like |0,2>+|2,0> are discussed and in
far off resonance case generation of entangled state of two coherent states is
discussed.Comment: 20 pages, 5 figures, revised version. submitted to Phys. Rev.
Single Photons on Pseudo-Demand from Stored Parametric Down-Conversion
We describe the results of a parametric down-conversion experiment in which
the detection of one photon of a pair causes the other photon to be switched
into a storage loop. The stored photon can then be switched out of the loop at
a later time chosen by the user, providing a single photon for potential use in
a variety of quantum information processing applications. Although the stored
single photon is only available at periodic time intervals, those times can be
chosen to match the cycle time of a quantum computer by using pulsed
down-conversion. The potential use of the storage loop as a photonic quantum
memory device is also discussed.Comment: 8 pages, 7 Figs., RevTe