Optimal demonstration of Autler Townes splitting

The atom-light interaction in a three-level system has shown significant physical phenomena, such as electromagnetically induced transparency and Autler{Townes splitting (ATS), for broad applications in classical and quantum information techniques. Here, we optimally demonstrated the ATS with a quantum state manipulation method. The ATS in the dephasing-dominated diamond NV center system was successfully recovered by coherent microwave control, which cannot be observed with traditional method. The dynamical process of ATS was investigated in detail, revealing a nontrivial quantum interference with geometric phase modulations. Based on the quantum interference, the signal of the optimal ATS is twice as intense as those with traditional observation method.Comment: 10 pages and 9 figure

Bunching Effect and Quantum Statistics of Partially Indistinguishable Photons

The quantum statistics of particles is determined by both the spins and the indistinguishability of quantum states. Here we studied the quantum statistics of partially distinguishable photons by defining the multi-photon indistinguishability. The photon bunching co-efficient was formulated based on the properties of permutation symmetry, and a modified Bose--Einstein statistics was presented with an indistinguishability induced photon bunching effect. Moreover, the statistical transition of the photon state was studied for partially distinguishable photons, and the results shows the that indistinguishability exhibits the same role as that observed in the generation of laser. The results will fill the gap between Bose--Einstein and Poisson statistics for photons, and a formula is presented for the study of multi-photon quantum information processes.Comment: 6 pages, 3 figure

Quantum statistical imaging of particles without restriction of the diffraction limit

A practical quantum measurement method based on the quantum nature of anti-bunching photon emission has been developed to detect single particles without the restriction of the diffraction limit. By simultane- ously counting the single-photon and two-photon signals with fluorescence microscopy, the images of nearby Nitrogen-Vacancy centers in diamond at a distance of 8.5+/-2.4 nm have been successfully reconstructed. Also their axes information was optically obtained. This quantum statistical imaging technique, with a simple exper- imental setup, can also be easily generalized in the measuring and distinguishing of other physical properties with any overlapping, which shows high potential in future image and study of coupled quantum systems for quantum information techniques.Comment: 5 figure

Machine Learning in/for Blockchain: Future and Challenges

Machine learning and blockchain are two of the most noticeable technologies in recent years. The first one is the foundation of artificial intelligence and big data, and the second one has significantly disrupted the financial industry. Both technologies are data-driven, and thus there are rapidly growing interests in integrating them for more secure and efficient data sharing and analysis. In this paper, we review the research on combining blockchain and machine learning technologies and demonstrate that they can collaborate efficiently and effectively. In the end, we point out some future directions and expect more researches on deeper integration of the two promising technologies

Dynamical Signature of Symmetry Fractionalization in Frustrated Magnets

The nontrivialness of quantum spin liquid (QSL) typically manifests in the non-local observables that signifies their existence, however, this fact actually casts shadow on detecting QSL with experimentally accessible probes. Here, we provide a solution by unbiasedly demonstrating dynamical signature of anyonic excitations and symmetry fractionalization in QSL. Employing large-scale quantum Monte Carlo simulation and stochastic analytic continuation, we investigate the extended XXZ model on the kagome lattice, and find out that across the phase transitions from Z2 QSLs to different symmetry breaking phases, spin spectral functions can reveal the presence and condensation of emergent anyonic spinon and vison excitations, in particular the translational symmetry fractionalization of the latter, which can be served as the unique dynamical signature of the seemingly ephemeral QSLs in spectroscopic techniques such as inelastic neutron or resonance (inelastic) X-ray scatterings.Comment: 8 pages,6 figure

Characterizing high-quality high-dimensional quantum key distribution by state mapping between different degree of freedoms

Quantum key distribution (QKD) guarantees the secure communication between legitimate parties with quantum mechanics. High-dimensional QKD (HDQKD) not only increases the secret key rate but also tolerates higher quantum bit error rate (QBER). Many HDQKD experiments have been realized by utilizing orbital-angular-momentum (OAM) photons as the degree of freedom (DOF) of OAM of the photon is a prospective resource for HD quantum information. In this work we proposed and characterized that a high-quality HDQKD based on polarization-OAM hybrid states can be realized by utilizing state mapping between different DOFs. Both the preparation and measurement procedures of the proof-of-principle verification experiment are simple and stable. Our experiment verified that $(0.60\pm 0.06)\%$ QBER and $1.849\pm 0.008$ bits secret key rate per sifted signal can be achieved for a four-dimensional QKD with the weak coherent light source and decoy state method.Comment: 5 figures, 2 table

Robust Majorana signature detection with a coupled quantum dot-nanomechanical resonator in all-optical domain

Motivated by a recent experiment [Nadj-Perge et al., Science 346, 602 (2014)] providing evidence for Majorana zero modes in iron chains on the superconducting Pb surface, in the present work, we theoretically propose an all-optical scheme to detect Majorana fermions, which is very different from the current tunneling measurement based on electrical means. The optical detection proposal consists of a quantum dot embedded in a nanomechanical resonator with optical pump-probe technology. With the optical means, the signal in the coherent optical spectrum presents a distinct signature for the existence of Majorana fermions in the end of iron chains. Further, the vibration of the nanomechanical resonator behaving as a phonon cavity will enhance the exciton resonance spectrum, which makes the Majorana fermions more sensitive to be detectable. This optical scheme affords a potential supplement for detection of Majorana fermions and supports to use Majorana fermions in Fe chains as qubits for potential applications in quantum computing devices.Comment: 20 pages, 4 figure

Controlled-phase manipulation module for orbital-angular-momentum photon states

Phase manipulation is essential to quantum information processing, for which the orbital angular momentum (OAM) of photon is a promising high-dimensional resource. Dove prism (DP) is one of the most important element to realize the nondestructive phase manipulation of OAM photons. DP usually changes the polarization of light and thus increases the manipulation error for a spin-OAM hybrid state. DP in a Sagnac interferometer also introduces a mode-dependent global phase to the OAM mode. In this work, we implemented a high-dimensional controlled-phase manipulation module (PMM), which can compensate the mode-dependent global phase and thus preserve the phase in the spin-OAM hybrid superposition state. The PMM is stable for free running and is suitable to realize the high-dimensional controlled-phase gate for spin-OAM hybrid states. Considering the Sagnac-based structure, the PMM is also suitable for classical communication with spin-OAM hybrid light field.Comment: 5 pages, 6 figure

Indistinguishability-induced classical-to-nonclassical transition of photon statistics

Photon statistics is one of the key properties of the photon state for the study of quantum coherence and quantum information techniques. Here, we discuss the photon indistinguishability induced bunching effect which can significantly change photon statistics. Through the measurement of the second-order degree of coherence of a mixed photon state composed of a single-photon state and a weak coherent state, the statistical transition from a classical behavior to a nonclassical behavior is experimentally demonstrated by modifying the indistinguishability of the two-photon states. The study will help us to understand and control the photon statistics with a method for quantum optical coherence and quantum information applications. It also indicates that the photon indistinguishability is a key parameter for multipartite quantum coherence.Comment: 5pages, 5 figure

High contrast quantum imaging with time-gated fluorescence detection

Optical detection of spin state has been widely used for the solid state spin qubit in the application of quantum information processing. The signal contrast determines the accuracy of quantum state manipulation, sensitivity of quantum sensing and resolution of quantum imaging. Here, we demonstrated a time-gated fluorescence detection method for enhancing the spin state signal contrast of nitrogen vacancy (NV) center in diamond. By adjusting the delay between time gate and the excitation laser pulse, we improved both the signal contrast and signal-to-noise ratio for NV spin detection. An enhancement ratio of 1.86 times was reached for the signal contrast. Utilizing the time-gated fluorescence detection, we further demonstrated a high contrast quantum imaging of nanoparticle's stray magnetic field. Without any additional manipulation of the quantum state, we expect that this method can be used to improve the performance of various applications with NV center