The implementation of polarization-based quantum communication is limited by signal loss and decoherence caused by the birefringence of a single-mode fiber. We investigate the Knill dynamical decoupling scheme, implemented using half-wave plates, to minimize decoherence and show that a fidelity greater than 99% can be achieved in absence of rotation error and fidelity greater than 96% can be achieved in presence of rotation error. Such a scheme can be used to preserve any quantum state with high fidelity and has potential application for constructing all optical quantum delay line, quantum memory, and quantum repeater.
Mach-Zehnder interferometry based on mixing the coherent and the squeezed vacuum states of light has Heisenberg limited capabilities for phase estimation. This is also, because the quantum Cramer-Rao bound on sensitivity of phase estimation with the above interferometric scheme reaches the Heisenberg limit when the inputs are mixed in hear equal proportions. We show that a detection strategy based on the measurement of parity of photon number in one of the output modes of the interferometer saturates the quantum Cramer-Rao bound of the interferometric scheme, and therefore- as a consequence- hits the Heisenberg limit when the inputs are mixed in equal intensities.
We show, by using parity detection, that the phase estimate obtained from the linear error propagation formula,
indeed saturates the lower bound set by maximizing quantum Fisher information for several of the well-known
states, proposed for the Heisenberg limited interferometry. Our results show that one can achieve the quantum
Cram´er-Rao bound, by simply counting the number of photons which is not very far from actual realization.
It has been known for a while that, provided by the Heisenberg Uncertainty Principle, certain types of quantum
correlated light should yield a better scaling law than the one with ordinary laser light. Hitherto, however,
there is no such device practically used outside laboratories. The fact that quantum correlations are easy to
be destroyed under decoherence essentially makes their utilities problematic for real world applications. For the
optical interferometers, the most significant decoherence phenomenon is the photon loss. And yet, there has been
no real-world device for quantum-enhanced sensing that overcomes the photon loss effects. In order to analyze
the photon loss effects the description of the quantum states of light calls for a density matrix formalism, rather
than the usual pure state approach. Here we take an example of the input states for the Heisenberg-limited
interferometry, namely the optimal state, and show the description of the quantum state of light based on the
reduced density matrix.
It is known that the phase measurement using lossless Mach-Zehnder interferometer with certain entangled
N-photon states can achieve a phase sensitivity of the order of 1/N, the Heisenberg limit. However, the output
observable used is different for different input states to achieve the Heisenberg limit. In this paper, we show
that it is possible to achieve this limit just by parity measurement for all the commonly proposed entangled
states. Taking account of path absorption effect, the phase shifts with parity measurement for these states are
obtained and indicate that the N00N state still remains to be the best candidate to perform phase detection if the
transmittance of the medium is not too small and the number of photons is not very large.
Quantum entanglement has the potential to revolutionize the entire field of interferometric sensing by providing
many orders of magnitude improvement in interferometer sensitivity. The quantum-entangled particle interferometer
approach is very general and applies to many types of interferometers. In particular, without nonlocal
entanglement, a generic classical interferometer has a statistical-sampling shot-noise limited sensitivity that scales
like 1/√N
N, where N is the number of particles passing through the interferometer per unit time. However, if
carefully prepared quantum correlations are engineered between the particles, then the interferometer sensitivity
improves by a factor of √N
to scale like 1/N, which is the limit imposed by the Heisenberg Uncertainty Principle.
For optical interferometers operating at milliwatts of optical power, this quantum sensitivity boost corresponds
to an eight-order-of-magnitude improvement of signal to noise. This effect can translate into a tremendous science
pay-off for space missions. For example, one application of this new effect is to fiber optical gyroscopes
for deep-space inertial guidance and tests of General Relativity (Gravity Probe B). Another application is to
ground and orbiting optical interferometers for gravity wave detection, Laser Interferometer Gravity Observatory
(LIGO) and the European Laser Interferometer Space Antenna (LISA), respectively. Other applications are to
Satellite-to-Satellite laser Interferometry (SSI) proposed for the next generation Gravity Recovery And Climate
Experiment (GRACE II).
Information science is entering into a new era in which certain subtleties of quantum mechanics enables large enhancements in computational efficiency and communication security. Naturally, precise control of quantum systems required for the implementation of quantum information processing protocols implies potential breakthoughs in other sciences and technologies. We discuss recent developments in quantum control in optical systems and their applications in metrology and imaging.
Quantum entanglement has the potential to revolutionize the entire field of interferometric sensing by providing many orders of magnitude improvement in interferometer sensitivity. The quantum entangled particle interferometer approach is very general and applies to many types of interferometers. In particular, without nonlocal entanglement, a generic classical interferometer has a statistical-sampling shot-noise limited sensitivity that scales like 1/√N, where N is the number of particles passing through the interferometer per unit time. However, if carefully prepared quantum correlations are engineered between the particles, then the interferometer sensitivity improves by a factor of √N to scale like 1/N, which is the limit imposed by the Heisenberg Uncertainty Principle. For optical interferometers operating at milliwatts of optical power, this quantum sensitivity boost corresponds to an eight-order-of-magnitude improvement of signal to noise. This effect can translate into a tremendous science pay-off for NASA-JPL missions. For example, one application of this new effect is to fiber optical gyroscopes for deep-space inertial guidance and tests of General Relativity (Gravity Probe B). Another application is to ground and orbiting optical interferometers for gravity wave detection, Laser Interferometer Gravity Observatory (LIGO) and the European Laser Interferometer Space Antenna (LISA), respectively. Other applications are to Satellite-to-Satellite laser Interferometry (SSI) proposed for the next generation Gravity Recovery And Climate Experiment (GRACE II).
The technique of projective measurements in linear optics can provide apparent, efficient nonlinear interaction between photons, which is technically problematic otherwise. We present an application of such a technique to prepare large photon-number path entanglement. Large photon-number path entanglement is an important resource for Heisenberg-limited optical interferometry, where the sensitivity of phase measurements can be improved beyond the usual shot-noise limit. A similar technique can also be applied to signal the presence of a single photon without destroying it. We further show how to build a quantum repeater for long-distance quantum communication.
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