266 research outputs found
Schr\"odinger's cat in an optical sideband
We propose a method to subtract a photon from a double sideband mode of
continuous-wave light. The central idea is to use phase modulation as a
frequency sideband beamsplitter in the heralding photon subtraction scheme,
where a small portion of the sideband mode is downconverted to the carrier
frequency to provide a trigger photon. An optical Schr\"odinger's cat state is
created by applying the propesed method to a squeezed state at 500MHz sideband,
which is generated by an optical parametric oscillator. The Wigner function of
the cat state reconstructed from a direct homodyne measurement of the 500MHz
sideband modes shows the negativity of without any
loss corrections.Comment: 11 pages, 9 figure
Sequential Quantum Teleportation of Optical Coherent States
We demonstrate a sequence of two quantum teleportations of optical coherent
states, combining two high-fidelity teleporters for continuous variables. In
our experiment, the individual teleportation fidelities are evaluated as F_1 =
0.70 \pm 0.02 and F_2 = 0.75 \pm 0.02, while the fidelity between the input and
the sequentially teleported states is determined as F^{(2)} = 0.57 \pm 0.02.
This still exceeds the optimal fidelity of one half for classical teleportation
of arbitrary coherent states and almost attains the value of the first
(unsequential) quantum teleportation experiment with optical coherent states.Comment: 5page, 4figure
Characterization of entangling properties of quantum measurement via two-mode quantum detector tomography using coherent state probes
Entangled measurement is a crucial tool in quantum technology. We propose a
new entanglement measure of multi-mode detection, which estimates the amount of
entanglement that can be created in a measurement. To illustrate the proposed
measure, we perform quantum tomography of a two-mode detector that is comprised
of two superconducting nanowire single photon detectors. Our method utilizes
coherent states as probe states, which can be easily prepared with accuracy.
Our work shows that a separable state such as a coherent state is enough to
characterize a potentially entangled detector. We investigate the entangling
capability of the detector in various settings. Our proposed measure verifies
that the detector makes an entangled measurement under certain conditions, and
reveals the nature of the entangling properties of the detector. Since the
precise characterization of a detector is essential for applications in quantum
information technology, the experimental reconstruction of detector properties
along with the proposed measure will be key features in future quantum
information processing.Comment: 18 pages, 6 figure
Molecular-beam epitaxial growth of a far-infrared transparent electrode for extrinsic Germanium photoconductors
We have evaluated the optical and electrical properties of a far-infrared
(IR) transparent electrode for extrinsic germanium (Ge) photoconductors at 4 K,
which was fabricated by molecular beam epitaxy (MBE). As a far-IR transparent
electrode, an aluminum (Al)-doped Ge layer is formed at well-optimized doping
concentration and layer thickness in terms of the three requirements: high
far-IR transmittance, low resistivity, and excellent ohmic contact. The
Al-doped Ge layer has the far-IR transmittance of >95 % within the wavelength
range of 40--200 microns, while low resistivity (~5 ohm-cm) and ohmic contact
are ensured at 4 K. We demonstrate the applicability of the MBE technology in
fabricating the far-IR transparent electrode satisfying the above requirements.Comment: 18 pages, 7 figures, accepted for publication in the PAS
Quantum teleportation in space and frequency using entangled pairs of photons from a frequency comb
Using entangled pairs of photons from a frequency comb and wide-band frequency-resolved homodyne detection, we propose a sequential quantum teleportation protocol for continuous variables that teleports an unknown state in space and frequency. A subthreshold optical parametric oscillator (OPO) produces a comb of entangled pairs of photons separated by the free spectral range of the OPO cavity. Wide-band frequency-resolved homodyne detection enables direct access to the sum and difference of quadratures between different teeth in the comb. Such measurements are Einstein-Podolsky-Rosen nullifiers, and can be used as the basis for teleportation protocols. Our protocol for space-and-frequency teleportation effectively links arbitrary frequency channels for frequency-division multiplexing, which has applications in universal quantum computation and large-capacity quantum communication. © 2014 American Physical Society
Nonlinear Responses of Electronic-Excitation-Induced Phase Transformations in GaSb Nanoparticles
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