Exploiting boundary states of imperfect spin chains for high-fidelity state transfer
M. Bruderer, K. Franke, S. Ragg, W. Belzig, and D. Obreschkow
We study transfer of a quantum state through XX spin chains with static imperfections. We combine the two standard approaches for state transfer based on (i) modulated couplings between neighboring spins throughout the spin chain and (ii) weak coupling of the outermost spins to an unmodulated spin c ... [Phys. Rev. A 85, 022312 ] published .
Compact Continuous-Variable Entanglement Distillation
Animesh Datta, Lijian Zhang, Joshua Nunn, Nathan K. Langford, Alvaro Feito et al.
We introduce a new scheme for continuous-variable entanglement distillation that requires only linear temporal and constant physical or spatial resources. Distillation is the process by which high-quality entanglement may be distributed between distant nodes of a network in the unavoidable presence ... [Phys. Rev. Lett. 108, 060502 ] published .
Optimal nonlocal multipartite entanglement concentration based on projection measurements
Fu-Guo Deng
We propose an optimal nonlocal entanglement concentration protocol (ECP) for multiphoton systems in a partially entangled pure state, resorting to the projection measurement on an additional photon. One party in quantum communication first performs a parity-check measurement on her photon in an N-ph ... [Phys. Rev. A 85, 022311 ] published .
Optomechanical systems as single-photon routers
G. S. Agarwal and Sumei Huang
We theoretically demonstrate the possibility of using nanomechanical systems as single-photon routers. We show how electromagnetically induced transparency in cavity optomechanical systems can be used to produce a switch for a probe field in a single-photon Fock state using very low pumping powers o ... [Phys. Rev. A 85, 021801 ] published .
Optimal teleportation with a noisy source
B. G. Taketani, F. de Melo, and R. L. de Matos Filho
We establish the optimal quantum teleportation protocol for the realistic scenario where both the input state and quantum channel are afflicted by noise. By taking these effects into account, higher fidelities are achieved. The optimality of the proposed protocol prevails even when restricted to a r ... [Phys. Rev. A 85, 020301 ] published .
Quantum One-Time Pad in the Presence of an Eavesdropper
Fernando G. S. L. Brandao and Jonathan Oppenheim
A classical one-time pad allows two parties to send private messages over a public classical channelan eavesdropper who intercepts the communication learns nothing about the message. A quantum one-time pad is a shared quantum state which allows two parties to send private messages or private quantum ... [Phys. Rev. Lett. 108, 040504 ] published .
When Does Noise Increase the Quantum Capacity?
Fernando G. S. L. Brandao, Jonathan Oppenheim, and Sergii Strelchuk
Superactivation is the property that two channels with zero quantum capacity can be used together to yield a positive capacity. Here we demonstrate that this effect exists for a wide class of inequivalent channels, none of which can simulate each other. We also consider the case where one of two zer ... [Phys. Rev. Lett. 108, 040501 ] published .
Quantum linear amplifier enhanced by photon subtraction and addition
Ho-Joon Kim, Su-Yong Lee, Se-Wan Ji, and Hyunchul Nha
A deterministic quantum amplifier inevitably adds noise to an amplified signal due to the uncertainty principle in quantum physics. We here investigate how a quantum-noise-limited amplifier can be improved by additionally employing the photon subtraction, the photon addition, and a coherent superpos ... [Phys. Rev. A 85, 013839 ] published .
Generalized channels: Channels for convex subsets of the state space
Anna JenCova
Let K be a convex subset of the state space of a finite-dimensional C*-algebra. We study the properties of channels on K, which are defined as affine maps from K into the state space of another algebra, extending to completely positive maps on the subspace generated by K. We show that each such map ... [J. Math. Phys. 53, 012201 (2012)] published Wed Jan 25, 2012.
Master Equations for Correlated Quantum Channels
V. Giovannetti and G. M. Palma
We derive the general form of a master equation describing the reduced time evolution of a sequence of subsystems propagating in an environment which can be described as a sequence of subenvironments. The interaction between subsystems and subenvironments is described in terms of a collision model, ... [Phys. Rev. Lett. 108, 040401 ] published .
How to construct spin chains with perfect state transfer
Luc Vinet and Alexei Zhedanov
A method to systematically construct the XX quantum spin chains with nearest-neighbor interactions that allow perfect state transfer (PST) is shown. Sets of orthogonal polynomials (OPs) are in correspondence with such systems. The key observation is that for any admissible one-excitation energy spec ... [Phys. Rev. A 85, 012323 ] published .
Gaussian matrix-product states for coding in bosonic communication channels
Joachim Schafer, Evgueni Karpov, and Nicolas J. Cerf
The communication capacity of Gaussian bosonic channels with memory has recently attracted much interest. Here, we investigate a method to prepare the multimode entangled input symbol states for encoding classical information into these channels. In particular, we study the usefulness of a Gaussian ... [Phys. Rev. A 85, 012322 ] published .
Removing correlations in signals transmitted over a quantum memory channel
Cosmo Lupo, Laleh Memarzadeh, and Stefano Mancini
We consider a model of a bosonic memory channel, which induces correlations among the transmitted signals. The application of suitable unitary transformations at the encoding and decoding stages allows the complete removal of correlations, thereby mapping the memory channel into a memoryless one. Ho ... [Phys. Rev. A 85, 012320 ] published .
Spin chains for robust state transfer: Modified boundary couplings versus completely engineered chains
Analia Zwick, Gonzalo A. Alvarez, Joachim Stolze, and Omar Osenda
Quantum state transfer in the presence of static disorder and noise is one of the main challenges in building quantum computers. We compare the quantum state transfer properties for two classes of qubit chains under the influence of static disorder. In fully engineered chains all nearest-neighbor co ... [Phys. Rev. A 85, 012318 ] published .
Schemes of transmission of classical information via quantum channels with many senders: Discrete- and continuous-variable cases
L. Czekaj, J. K. Korbicz, R. W. Chhajlany, and P. Horodecki
Superadditivity effects in the classical capacity of discrete multiaccess channels and continuous variable (CV) Gaussian MACs are analyzed. Several examples of the manifestation of superadditivity in the discrete case are provided, including, in particular, a channel which is fully symmetric with re ... [Phys. Rev. A 85, 012316 ] published .
Perfect state transfer in [script PT]-symmetric non-Hermitian networks
X. Z. Zhang, L. Jin, and Z. Song
We systematically study the parity- and time-reversal ([script PT]) symmetric non-Hermitian version of a quantum network proposed in the paper of Christandl et al. [Phys. Rev. Lett. 92, 187902 (2004)]. The nature of this model shows that it is a paradigm to demonstrate the complex relationship bet ... [Phys. Rev. A 85, 012106 ] published .
Achievable qubit rates for quantum-information wires
Hulya Yadsan-Appleby and Tobias J. Osborne
Suppose Alice and Bob have access to two separated regions, respectively, of a system of electrons moving in the presence of a regular one-dimensional lattice of binding atoms. We consider the problem of communicating as much quantum information, as measured by the qubit rate, through this quantum-i ... [Phys. Rev. A 85, 012310 ] published .
Theory of control of optomechanical transducers for quantum networks
Fang-Yu Hong, Yang Xiang, W. H. Tang, Zhi-Yan Zhu, Li-zhen Jiang et al.
We present a scheme of control for the arbitrary optical interface mediated by a nanoscale mechanical oscillator between flying qubits and optical nonactive solid-state qubits. This quantum interface lays the foundation for many key functions of a quantum network, such as transferring, swapping, and ... [Phys. Rev. A 85, 012309 ] published .
Optimal path for a quantum teleportation protocol in entangled networks
C. Di Franco and D. Ballester
Bellman's optimality principle has been of enormous importance in the development of whole branches of applied mathematics, computer science, optimal control theory, economics, decision making, and classical physics. Examples are numerous: dynamic programming, Markov chains, stochastic dynamics, cal ... [Phys. Rev. A 85, 010303 ] published .
Spin Guides and Spin Splitters: Waveguide Analogies in One-Dimensional Spin Chains
Melissa I. Makin, Jared H. Cole, Charles D. Hill, and Andrew D. Greentree
Here we show a mapping between waveguide theory and spin-chain transport, opening an alternative approach to solid-state quantum information transport. By applying temporally varying control profiles to a spin chain, we design a virtual waveguide or spin guide to conduct spin excitations along defin ... [Phys. Rev. Lett. 108, 017207 ] published .
Efficient single-photon-assisted entanglement concentration for partially entangled photon pairs
Yu-Bo Sheng, Lan Zhou, Sheng-Mei Zhao, and Bao-Yu Zheng
We present two realistic entanglement concentration protocols (ECPs) for pure partially entangled photons. A partially entangled photon pair can be concentrated to a maximally entangled pair with only an ancillary single photon with a certain probability, while the conventional ECPs require two copi ... [Phys. Rev. A 85, 012307 ] published .