results for au:Hu_T in:quant-ph

- Jan 16 2018 quant-ph arXiv:1801.04418v1We perform decoy-state quantum key distribution between a low-Earth-orbit satellite and multiple ground stations located in Xinglong, Nanshan, and Graz, which establish satellite-to-ground secure keys with ~kHz rate per passage of the satellite Micius over a ground station. The satellite thus establishes a secure key between itself and, say, Xinglong, and another key between itself and, say, Graz. Then, upon request from the ground command, Micius acts as a trusted relay. It performs bitwise exclusive OR operations between the two keys and relays the result to one of the ground stations. That way, a secret key is created between China and Europe at locations separated by 7600 km on Earth. These keys are then used for intercontinental quantum-secured communication. This was on the one hand the transmission of images in a one-time pad configuration from China to Austria as well as from Austria to China. Also, a videoconference was performed between the Austrian Academy of Sciences and the Chinese Academy of Sciences, which also included a 280 km optical ground connection between Xinglong and Beijing. Our work points towards an efficient solution for an ultralong-distance global quantum network, laying the groundwork for a future quantum internet.
- Quantum key distribution (QKD) uses individual light quanta in quantum superposition states to guarantee unconditional communication security between distant parties. In practice, the achievable distance for QKD has been limited to a few hundred kilometers, due to the channel loss of fibers or terrestrial free space that exponentially reduced the photon rate. Satellite-based QKD promises to establish a global-scale quantum network by exploiting the negligible photon loss and decoherence in the empty out space. Here, we develop and launch a low-Earth-orbit satellite to implement decoy-state QKD with over kHz key rate from the satellite to ground over a distance up to 1200 km, which is up to 20 orders of magnitudes more efficient than that expected using an optical fiber (with 0.2 dB/km loss) of the same length. The establishment of a reliable and efficient space-to-ground link for faithful quantum state transmission constitutes a key milestone for global-scale quantum networks.
- Dec 10 2010 quant-ph arXiv:1012.1994v2In this paper, a (3\times3)-matrix representation of the Birman-Wenzl-Murakami(BWM) algebra has been presented. Based on which, unitary matrices (A(\theta,\phi_1,\phi_2), B(\theta,\phi_1,\phi_2)) are generated via the Yang-Baxterization approach. A hamiltonian is constructed from the unitary (B(\theta,\phi)) matrix. We then study the Berry phase of the Yang-Baxter system and find the topological parameter d has relationship with berry phase.
- Apr 24 2009 quant-ph arXiv:0904.3621v1In this paper we construct a new $8\times8$ $\mathbb{M}$ matrix from the $4\times4$ $M$ matrix, where $\mathbb{M}$ / $M$ is the image of the braid group representation. The $ 8\times8 $ $\mathbb{M}$ matrix and the $4\times4$ $M$ matrix both satisfy extraspecial 2-groups algebra relations. By Yang-Baxteration approach, we derive a unitary $ \breve{R}(\theta, \phi)$ matrix from the $\mathbb{M}$ matrix with parameters $\phi$ and $\theta$. Three-qubit entangled states can be generated by using the $\breve{R}(\theta,\phi)$ matrix. A Hamiltonian for 3 qubits is constructed from the unitary $\breve{R}(\theta,\phi)$ matrix. We then study the entanglement and Berry phase of the Yang-Baxter system.
- Apr 02 2009 quant-ph arXiv:0904.0090v4A method of constructing Temperley-Lieb algebras(TLA) representations has been introduced in [Xue \emphet.al arXiv:0903.3711]. Using this method, we can obtain another series of $n^{2}\times n^{2}$ matrices $U$ which satisfy the TLA with the single loop $d=\sqrt{n}$. Specifically, we present a $9\times9$ matrix $U$ with $d=\sqrt{3}$. Via Yang-Baxterization approach, we obtain a unitary $ \breve{R}(\theta ,\varphi_{1},\varphi_{2})$-matrix, a solution of the Yang-Baxter Equation. This $9\times9$ Yang-Baxter matrix is universal for quantum computing.
- Mar 31 2009 quant-ph arXiv:0903.5230v4In this paper we present reducible representation of the $n^{2}$ braid group representation which is constructed on the tensor product of n-dimensional spaces. By some combining methods we can construct more arbitrary $n^{2}$ dimensional braiding matrix S which satisfy the braid relations, and we get some useful braiding matrix S. By Yang-Baxteraition approach, we derive a $ 9\times9 $ unitary $ \breve{R}$ according to a $ 9\times9 $ braiding S-matrix we have constructed. The entanglement properties of $ \breve{R}$-matrix is investigated, and the arbitrary degree of entanglement for two-qutrit entangled states can be generated via $ \breve{R}(\theta, \phi_{1},\phi_{2})$-matrix acting on the standard basis.
- Mar 24 2009 quant-ph arXiv:0903.3711v6A method of constructing $n^{2}\times n^{2}$ matrix solutions(with $n^{3}$ matrix elements) of Temperley-Lieb algebra relation is presented in this paper. The single loop of these solutions are $d=\sqrt{n}$. Especially, a $9\times9-$matrix solution with single loop d=$\sqrt{3}$ is discussed in detail. An unitary Yang-Baxter $\breve{R}(\theta,q_{1},q_{2})$ matrix is obtained via the Yang-Baxterization process. The entanglement property and geometric property (\emphi.e. Berry Phase) of this Yang-Baxter system are explored.