7 research outputs found
Experimental implementation of a Kochen-Specker set of quantum tests
The conflict between classical and quantum physics can be identified through
a series of yes-no tests on quantum systems, without it being necessary that
these systems be in special quantum states. Kochen-Specker (KS) sets of yes-no
tests have this property and provide a quantum-versus-classical advantage that
is free of the initialization problem that affects some quantum computers.
Here, we report the first experimental implementation of a complete KS set that
consists of 18 yes-no tests on four-dimensional quantum systems and show how to
use the KS set to obtain a state-independent quantum advantage. We first
demonstrate the unique power of this KS set for solving a task while avoiding
the problem of state initialization. Such a demonstration is done by showing
that, for 28 different quantum states encoded in the orbital-angular-momentum
and polarization degrees of freedom of single photons, the KS set provides an
impossible-to-beat solution. In a second experiment, we generate maximally
contextual quantum correlations by performing compatible sequential
measurements of the polarization and path of single photons. In this case,
state independence is demonstrated for 15 different initial states. Maximum
contextuality and state independence follow from the fact that the sequences of
measurements project any initial quantum state onto one of the KS set's
eigenstates. Our results show that KS sets can be used for quantum-information
processing and quantum computation and pave the way for future developments.Comment: REVTeX, 15 pages, 4 figure
Photon bunching in parametric down-conversion with continuous wave excitation
The first direct measurement of photon bunching (g2 correlation function) in
one output arm of a spontaneous-parametric-down-conversion source operated with
a continuous pump laser in the single-photon regime is demonstrated. The result
is in agreement with the statistics of a thermal field of the same coherence
length, and shows the feasibility of investigating photon statistics with
compact cw-pumped sources. Implications for entanglement-based quantum
cryptography are discussed.Comment: 7 pages, 4 figures, expanded introduction and experimental details
added. Accepted for publication in Phys.Rev.
The Status of the Wave Function in Dynamical Collapse Models
The idea that in dynamical wave function collapse models the wave function is
superfluous is investigated. Evidence is presented for the conjecture that, in
a model of a field theory on a 1+1 lightcone lattice, knowing the field
configuration on the lattice back to some time in the past, allows the wave
function or quantum state at the present moment to be calculated, to arbitrary
accuracy so long as enough of the past field configuration is known.Comment: 35 pages, 11 figures, LaTex, corrected typos, some modifications
made. to appear in Found. of Phys. Lett. Vol. 18, Nbr 6, Nov 2005, 499-51
Simulating causal collapse models
We present simulations of causal dynamical collapse models of field theories
on a 1+1 null lattice. We use our simulations to compare and contrast two
possible interpretations of the models, one in which the field values are real
and the other in which the state vector is real. We suggest that a procedure of
coarse graining and renormalising the fundamental field can overcome its
noisiness and argue that this coarse grained renormalised field will show
interesting structure if the state vector does on the coarse grained scale.Comment: 18 pages, 8 fugures, LaTeX, Reference added, discussion of
probability distribution of labellings correcte