15 research outputs found
Coherent and Squeezed Vacuum Light Interferometry: Parity detection hits the Heisenberg limit
The interference between coherent and squeezed vacuum light can produce path
entangled states with very high fidelities. We show that the phase sensitivity
of the above interferometric scheme with parity detection saturates the quantum
Cramer-Rao bound, which reaches the Heisenberg-limit when the coherent and
squeezed vacuum light are mixed in roughly equal proportions. For the same
interferometric scheme, we draw a detailed comparison between parity detection
and a symmetric-logarithmic-derivative-based detection scheme suggested by Ono
and Hofmann.Comment: Change in the format from aps to iop since we decided to submit it to
NJP; Minor changes in tex
Measurement of two independent phase-shifts using coupled parametric amplifiers
In this article, we demonstrate a scheme capable of two-phase measurement,
i.e. the simultaneous measurement of the two phase-shifts occurring in two
independent Mach-Zehnder interferometers using one intensity detector. Our
scheme utilizes dark-state-enhanced coupled parametric amplifiers in an atomic
medium to mix the multiple fields probing the various arms of the
interferometers in parallel. The two phase-differences are then encoded in
separate continuous-variable parameters in the spectral waveform of the
parametrically amplified atom-radiated signal field, which can be directly
decoupled in a single intensity measurement. Besides resolving two phase
differences in parallel, this method can also be used to increase the channel
capacity in optical and quantum communication by the simultaneous use of
phase-modulation and amplitude-modulation.Comment: 8 pages, 4 figure
Thermal quantum metrology in memoryless and correlated environments
In bosonic quantum metrology, the estimate of a loss parameter is typically performed by means of pure states, such as coherent, squeezed or entangled states, while mixed thermal probes are discarded for their inferior performance. Here we show that thermal sources with suitable correlations can be engineered in such a way to approach, or even surpass, the error scaling of coherent states in the presence of general Gaussian decoherence. Our findings pave the way for practical quantum metrology with thermal sources in optical instruments (e.g., photometers) or at different wavelengths (e.g., far infrared, microwave or X-ray) where the generation of quantum features, such as coherence, squeezing or entanglement, may be extremely challenging
Improving the phase super-sensitivity of squeezing-assisted interferometers by squeeze factor unbalancing
The sensitivity properties of an SU(1,1) interferometer made of two cascaded
parametric amplifiers, as well as of an ordinary SU(2) interferometer preceded
by a squeezer and followed by an anti-squeezer, are theoretically investigated.
Several possible experimental configurations are considered, such as the
absence or presence of a seed beam, direct or homodyne detection scheme. In all
cases we formulate the optimal conditions to achieve phase super-sensitivity,
meaning a sensitivity overcoming the shot-noise limit. We show that for a given
gain of the first parametric amplifier, unbalancing the interferometer by
increasing the gain of the second amplifier improves the interferometer
properties. In particular, a broader super-sensitivity phase range and a better
overall sensitivity can be achieved by gain unbalancing.Comment: 14 pages, 14 figure
Two-mode squeezed vacuum: Phase estimation and parity detection
We present a parity-measurement-based phase estimation protocol with two-mode squeezed vacuum states; effects of loss and excess noise in squeezed vacuum are discussed; and a parity detection scheme without number-resolving detectors is proposed. © 2010 Optical Society of America