Single-photon Channel Research Articles

Research on joint coding for underwater single-photon video communication

In order to achieve effective and reliable video transmission, a video joint coding scheme based on dictionary learning and the concatenation of LT code and LDPC code is proposed for underwater single-photon com-munication system. Sparse coding based on dictionary learning greatly compresses the amount of video data. According to the deletion characteristic of underwater single-photon channel, using the LT-LDPC channel concatenated coding method can overcome the disadvantage of excessive decoding overhead of LT code. Aiming at the problem of decoding failure probability of LT coding, a double feedback mechanism for decoding success is proposed. The experimental results show that when the channel error rate is in the order of 10-2 and the video compression rate is 75.6%, the video frames can be reconstructed with an average peak signal-to-noise ratio (PSNR) of 37.4921 dB.

Quantum communication using code division multiple access network

For combining different single photon channels into single path, we use an effective and reliable technique which is known as quantum multiple access. We take advantage of an add-drop multiplexer capable of pushing and withdrawing a single photon into an optical fiber cable which carries quantum bits from multiusers. In addition to this, spreading spreads the channel noise at receiver side and use of filters stop the overlapping of adjacent channels, which helps in reducing the noise level and improved signal-to-noise ratio. In this way, we obtain enhanced performance of code division multiple access-based QKD links with a single photon without necessity of amplifiers and modulators.

Detection of Lipase Activity in Cells by a Fluorescent Probe Based on Formation of Self-Assembled Micelles.

SummaryReliable and sensitive detection of lipase activity is essential for the early diagnosis and monitoring of acute pancreatitis or progression of digestive diseases. However, the available fluorescent probes for detection of lipase activity are only implemented in a hexane-water two-phase system due to the nature of heterogeneous catalysis of lipase, thus limiting their applications in direct imaging of lipase activity in living cells and tissues. Here we designed and synthesized a “turn on” fluorescent probe CPP based on self-assembled micelles for hydrolysis of lipase. The CPP probe exhibits high selectivity and excellent sensitivity for the detection of lipase in such a homogeneous system and is successfully applied for monitoring lipase activity in pancreatic AR42J cells, tissues, and serums. Taken together, the fluorescent CPP probe not only provides a tool for diagnostic potential in pancreatic disease but also demonstrates an application potential for micelle self-assembly-based development of biological probes.

Strategy for single-shot CH3 imaging in premixed methane/air flames using photofragmentation laser-induced fluorescence

Single-shot imaging of methyl radical (CH3) in premixed methane/air flames is demonstrated using photofragmentation laser-induced fluorescence (PF-LIF) technique. A pump-probe strategy was adopted with the pump laser at 212.8 nm photolyzing CH3, and with the probe laser at 426.8 nm detecting the photolyzed CH (X2Π) fragments. Spatially resolved spectrograph of the PF-LIF signal from a stable laminar flame was recorded across the reaction zone to investigate potential interferences. The results indicate that the single-photon channel, CH3 + 212.8 nm → CH (X2Π) + H2, dominates the photofragmentation process. The CH2 radical was excluded from being an interfering precursor of the CH (X2Π) fragments owing to its relatively low concentration and small absorption cross section. Naturally present CH in the flame was identified as the main interference, but was conservatively estimated to account for only less than 4% of the total PF-LIF signal. Signal-to-noise ratio of around 10 was realized for single-shot imaging of natural CH3 in turbulent jet flames.

Quantum Spread Spectrum Multiple Access

We describe a quantum multiple access scheme that can take separate single photon channels and combine them in the same path. We propose an add-drop multiplexer that can insert or extract a single photon into an optical fiber carrying the qubits of all the other users. The system follows the principle of code division multiple access, a spread spectrum technique widely used in cellular networks.

Brane worlds at the LHC: Branons and KK gravitons

We study the possibility of testing some generic properties of Brane-World scenarios at the LHC. In particular, we pay attention to KK-graviton and branon production. Both signals can be dominant depending on the value of the brane tension. We analyze the differences between these two signatures. Finally, we use recent data in the single photon channel from the ATLAS collaboration to constraint the parameter space of both phenomenologies.

Improved Timing Resolution Single-Photon Detectors in Daytime Free-Space Quantum Key Distribution With 1.25 GHz Transmission Rate

In free-space single-photon quantum key distribution (QKD), the error rate due to daytime background photons can be reduced with strong temporal filtering. In this case, the improvement in performance is determined by the receiver's ability to resolve signal-photon arrival times. We use fast clock recovery and commercially available single-photon detectors with timing resolution enhanced by additional electronic circuitry to implement temporal gating down to 50 ps in a free-space QKD system. The single-photon channel operates at 850 nm, and the improved timing resolution enables transmission rates of 1.25 GHz. We observe daytime quantum bit error rates of 0.04, which is less than one-third of the ungated error rate. We present the design and performance of the system and demonstrate its benefit to free-space QKD.

Branon search in hadronic colliders

In the context of the brane-world scenarios with compactified extra dimensions, we study the production of brane fluctuations (branons) in hadron colliders ($p\overline{p}$, $pp$, and ${e}^{\ifmmode\pm\else\textpm\fi{}}p$) in terms of the brane tension parameter $f$, the branon mass $M$, and the number of branons $N$. From the absence of monojet events at HERA and Tevatron (run I), we set bounds on these parameters and we also study how such bounds could be improved at Tevatron (run II) and the future LHC. The single-photon channel is also analyzed for the two last colliders.

Inelastic wave mixing and multi-photon destructive interference based induced transparency in coherently prepared media

We consider a multi-level medium initially prepared with a coherent superposition of two initial levels that are not directly dipole-coupled. We study the production of multi-wave mixing in the coherent medium, where the process begins on one and terminates on the other of the two prepared levels. We find that a new type of wave mixing field can be efficiently generated in such a system with characteristics of both conventional four-wave mixing and stimulated hyper-Raman emission. We also show that two multi-photon destructive interferences build up simultaneously, leading to simultaneous reduction of the attenuation of the pump and wave-mixing fields. As a consequence a pair of ultra slow, temporally and group-velocity matched pump and wave-mixing fields can be generated. This type of multi-photon induced transparency and its consequences are qualitatively different from the conventional EIT where the destructive interference occurs between two single photon channels.

Photodissociation of Bromoform at 248 nm: Single and Multiphoton Processes

We have performed photodissociation experiments on CHBr 3 at 248 nm using VUV ionization photofragment translational spectroscopy. Prompt C-Br bond fission is the dominant single-photon dissociation channel. In addition to primary Br and CHBr 2 signals, we observe Br, CHBr, CBr, HBr, and Br 2 products attributed to secondary photodissociation of CHBr 2 and CHBr. There are three competing fragmentation channels from the photodissociation of CHBr 2 : CHBr + Br, CH + Br 2 , and CBr + HBr. The conclusion that Br 2 fragments do not arise from a single-photon channel in appreciable yield is supported by transient FM absorption measurements of the CHBr radical. Because the molecular HBr and Br 2 detachment channels are multiphoton processes, they will have very little impact on the atmospheric chemistry of CHBr 3 . We conclude that the most important photodissociation channel of CHBr 3 in the UV region is C-Br bond breaking.

Observation of field phase dependent autoionization

We report on the observation of a field phase dependent autoionization rate of calcium in the region of the doubly excited state. Excitation of the autoionizing state occurs from the atomic ground state through two phase related and hence interfering channels, namely a three photon channel and a single photon channel , being the third harmonic of . The autoionization rate exhibits a sinusoidal modulation as a function of the relative phase of the two excitation fields. Both ionizing fields are not focused in the interaction region, thus demonstrating the possibility of phase control in a large interaction volume and free of phase shift effects associated with focused geometries.