122 research outputs found
Updating the Born rule
Despite the tremendous empirical success of quantum theory there is still
widespread disagreement about what it can tell us about the nature of the
world. A central question is whether the theory is about our knowledge of
reality, or a direct statement about reality itself. Regardless of their stance
on this question, current interpretations of quantum theory regard the Born
rule as fundamental and add an independent state-update (or "collapse") rule to
describe how quantum states change upon measurement. In this paper we present
an alternative perspective and derive a probability rule that subsumes both the
Born rule and the collapse rule. We show that this more fundamental probability
rule can provide a rigorous foundation for informational, or "knowledge-based",
interpretations of quantum theory.Comment: 6+2 pages; 3 figure
Communicating continuous quantum variables between different Lorentz frames
We show how to communicate Heisenberg-limited continuous (quantum) variables
between Alice and Bob in the case where they occupy two inertial reference
frames that differ by an unknown Lorentz boost. There are two effects that need
to be overcome: the Doppler shift and the absence of synchronized clocks.
Furthermore, we show how Alice and Bob can share Doppler-invariant
entanglement, and we demonstrate that the protocol is robust under photon loss.Comment: 4 pages, 1 figur
Heuristic for estimation of multiqubit genuine multipartite entanglement
For every N-qubit density matrix written in the computational basis, an
associated "X-density matrix" can be obtained by vanishing all entries out of
the main- and anti-diagonals. It is very simple to compute the genuine
multipartite (GM) concurrence of this associated N-qubit X-state, which,
moreover, lower bounds the GM-concurrence of the original (non-X) state. In
this paper, we rely on these facts to introduce and benchmark a heuristic for
estimating the GM-concurrence of an arbitrary multiqubit mixed state. By
explicitly considering two classes of mixed states, we illustrate that our
estimates are usually very close to the standard lower bound on the
GM-concurrence, being significantly easier to compute. In addition, while
evaluating the performance of our proposed heuristic, we provide the first
characterization of GM-entanglement in the steady states of the driven Dicke
model at zero temperature.Comment: 19 pages, 5 figure
Characterizing GHZ Correlations in Nondegenerate Parametric Oscillation via Phase Measurements
We present a potential realization of the Greenberger, Horne and Zeilinger ALL or NOTHING contradiction of quantum mechanics with local realism using phase measurement techniques in a simple photon number triplet. Such a triplet could be generated using nondegenerate parametric oscillation
Giant Kerr nonlinearities in Circuit-QED
The very small size of optical nonlinearities places wide ranging
restrictions on the types of novel physics one can explore. For an ensemble of
multi-level systems one can synthesize a large effective optical nonlinearity
using quantum coherence effects but such non-linearities are technically
extremely challenging to demonstrate at the single atom level. In this work we
describe how a single artificial multi-level Cooper Pair Box molecule,
interacting with a superconducting microwave coplanar waveguide resonator, when
suitably driven, can generate extremely large optical nonlinearities at
microwave frequencies, with no associated absorption. We describe how the giant
self-Kerr effect can be detected by measuring the second-order correlation
function and quadrature squeezing spectrum.Comment: 4 pages, 4 figures, 1 table; version accepted by PRL edito
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