631 research outputs found
Observation of bosonic coalescence of photon pairs
Quantum theory predicts that two indistinguishable photons incident on a
beam-splitter interferometer stick together as they exit the device (the pair
emerges randomly from one port or the other). We use a special
photon-number-resolving energy detector for a direct loophole-free observation
of this quantum-interference phenomenon. Simultaneous measurements from two
such detectors, one at each beam-splitter output port, confirm the absence of
cross-coincidences.Comment: 4 pages, 2 figures, submitted to Phys. Rev. Let
Tomography of photon-number resolving continuous-output detectors
We report a comprehensive approach to analysing continuous-output photon
detectors. We employ principal component analysis to maximise the information
extracted, followed by a novel noise-tolerant parameterised approach to the
tomography of PNRDs. We further propose a measure for rigorously quantifying a
detector's photon-number-resolving capability. Our approach applies to all
detectors with continuous-output signals. We illustrate our methods by applying
them to experimental data obtained from a transition-edge sensor (TES)
detector.Comment: 5 pages, 3 figures, also includes supplementary informatio
Temporal multimode storage of entangled photon pairs
Multiplexed quantum memories capable of storing and processing entangled
photons are essential for the development of quantum networks. In this context,
we demonstrate the simultaneous storage and retrieval of two entangled photons
inside a solid-state quantum memory and measure a temporal multimode capacity
of ten modes. This is achieved by producing two polarization entangled pairs
from parametric down conversion and mapping one photon of each pair onto a
rare-earth-ion doped (REID) crystal using the atomic frequency comb (AFC)
protocol. We develop a concept of indirect entanglement witnesses, which can be
used as Schmidt number witness, and we use it to experimentally certify the
presence of more than one entangled pair retrieved from the quantum memory. Our
work puts forward REID-AFC as a platform compatible with temporal multiplexing
of several entangled photon pairs along with a new entanglement certification
method useful for the characterisation of multiplexed quantum memories
Versatile silicon-waveguide supercontinuum for coherent mid-infrared spectroscopy
Infrared spectroscopy is a powerful tool for basic and applied science. The
molecular spectral fingerprints in the 3 um to 20 um region provide a means to
uniquely identify molecular structure for fundamental spectroscopy, atmospheric
chemistry, trace and hazardous gas detection, and biological microscopy. Driven
by such applications, the development of low-noise, coherent laser sources with
broad, tunable coverage is a topic of great interest. Laser frequency combs
possess a unique combination of precisely defined spectral lines and broad
bandwidth that can enable the above-mentioned applications. Here, we leverage
robust fabrication and geometrical dispersion engineering of silicon
nanophotonic waveguides for coherent frequency comb generation spanning 70 THz
in the mid-infrared (2.5 um to 6.2 um). Precise waveguide fabrication provides
significant spectral broadening and engineered spectra targeted at specific
mid-infrared bands. We use this coherent light source for dual-comb
spectroscopy at 5 um.Comment: 26 pages, 5 figure
Short-Wave Infrared Compressive Imaging of Single Photons
We present a short-wave infrared (SWIR) single photon camera based on a single superconducting nanowire single photon detector (SNSPD) and compressive imaging. We show SWIR single photon imaging at a megapixel resolution with a low signal-to-background ratio around 0.6, show SWIR video acquisition at 20 frames per second and 64x64 pixel video resolution, and demonstrate sub-nanosecond resolution time-of-flight imaging. All scenes were sampled by detecting only a small number of photons for each compressive sampling matrix. In principle, our technique can be used for imaging faint objects in the mid-IR regime
A V-to-F Substitution in SK2 Channels Causes Ca2+ Hypersensitivity and Improves Locomotion in a \u3cem\u3eC. elegans\u3c/em\u3e ALS Model
Small-conductance Ca2+-activated K+ (SK) channels mediate medium afterhyperpolarization in the neurons and play a key role in the regulation of neuronal excitability. SK channels are potential drug targets for ataxia and Amyotrophic Lateral Sclerosis (ALS). SK channels are activated exclusively by the Ca2+-bound calmodulin. Previously, we identified an intrinsically disordered fragment that is essential for the mechanical coupling between Ca2+/calmodulin binding and channel opening. Here, we report that substitution of a valine to phenylalanine (V407F) in the intrinsically disordered fragment caused a ~6 fold increase in the Ca2+ sensitivity of SK2-a channels. This substitution resulted in a novel interaction between the ectopic phenylalanine and M411, which stabilized PIP2-interacting residue K405, and subsequently enhanced Ca2+ sensitivity. Also, equivalent valine to phenylalanine substitutions in SK1 or SK3 channels conferred Ca2+ hypersensitivity. An equivalent phenylalanine substitution in the Caenorhabditis elegans (C. elegans) SK2 ortholog kcnl-2 partially rescued locomotion defects in an existing C. elegans ALS model, in which human SOD1G85R is expressed at high levels in neurons, confirming that this phenylalanine substitution impacts channel function in vivo. This work for the first time provides a critical reagent for future studies: an SK channel that is hypersensitive to Ca2+ with increased activity in vivo
Quantum Enigma Machine: Experimentally Demonstrating Quantum Data Locking
Shannon proved in 1949 that information-theoretic-secure encryption is possible if the encryption key is used only once, is random, and is at least as long as the message itself. Notwithstanding, when information is encoded in a quantum system, the phenomenon of quantum data locking allows one to encrypt a message with a shorter key and still provide information-theoretic security. We present one of the first feasible experimental demonstrations of quantum data locking for direct communication and propose a scheme for a quantum enigma machine that encrypts 6 bits per photon (containing messages, new encryption keys, and forward error correction bits) with less than 6 bits per photon of encryption key while remaining information-theoretically secure
- …