Distributed quantum sensing enhanced by continuous-variable error correction

A distributed sensing protocol uses a network of local sensing nodes to estimate a global feature of the network, such as a weighted average of locally detectable parameters. In the noiseless case, continuous-variable (CV) multipartite entanglement shared by the nodes can improve the precision of parameter estimation relative to the precision attainable by a network without shared entanglement; for an entangled protocol, the root mean square estimation error scales like 1/M with the number M of sensing nodes, the so-called Heisenberg scaling, while for protocols without entanglement, the error scales like 1√M. However, in the presence of loss and other noise sources, although multipartite entanglement still has some advantages for sensing displacements and phases, the scaling of the precision with M is less favorable. In this paper, we show that using CV error correction codes can enhance the robustness of sensing protocols against imperfections and reinstate Heisenberg scaling up to moderate values of M. Furthermore, while previous distributed sensing protocols could measure only a single quadrature, we construct a protocol in which both quadratures can be sensed simultaneously. Our work demonstrates the value of CV error correction codes in realistic sensing scenarios

Functional Renormalization for Chiral and U_A(1) Symmetries at Finite Temperature

We investigated the chiral symmetry and U_A(1) anomaly at finite temperature by applying the functional renormalization group to the SU(3) linear sigma model. Expanding the local potential around the classical fields, we derived the flow equations for the renormalization parameters. In chiral limit, the flow equation for the chiral condensate is decoupled from the others and can be analytically solved. The Goldstone theorem is guaranteed in vacuum and at finite temperature, and the two phase transitions for the chiral and U_A(1) symmetry restoration happen at the same critical temperature. In general case with explicit chiral symmetry breaking, the two symmetries are partially and slowly restored, and the scalar and pseudoscalar meson masses are controlled by the restoration in the limit of high temperature.Comment: 9 pages, 9figure

Environmental Kuznets Curves in the People’s Republic of China: turning points and regional differences

This paper examines the relationship between economic growth and environmental sustainability in the People’s Republic of China by empirically estimating environmental Kuznets curve (EKC) models using provincial-level panel data from 1985 to 2005. The results show that there exists an inverted-U shaped relationship as hypothesized by the EKC model between per capita income and per capita emissions (or discharges) in the cases of waste gas from fuel burning and waste water, with a turning point at per capita gross domestic product of $12,903 and$3,226, respectively, in 2005 purchasing power parity terms. This relationship does not hold in the case of waste gas from production or solid waste. The estimation results from the model allowing region-specific slope coefficients show that the EKCs of the more developed coastal region have a flatter rising portion with turning points occurring at a higher income level than those of the less developed central and western regions. The paper argues that this may reflect technology diffusion and leapfrogging and institution imitation across regions at different stages of development. Policy implications of these findings are discussed.environmental kuznets curve; EKC; China; economic growth; environmental sustainability

Voice Service Support in Mobile Ad Hoc Networks

Mobile ad hoc networks are expected to support voice traffic. The requirement for small delay and jitter of voice traffic poses a significant challenge for medium access control (MAC) in such networks. User mobility makes it more complex due to the associated dynamic path attenuation. In this paper, a MAC scheme for mobile ad hoc networks supporting voice traffic is proposed. With the aid of a low-power probe prior to DATA transmissions, resource reservation is achieved in a distributed manner, thus leading to small delay and jitter. The proposed scheme can automatically adapt to dynamic path attenuation in a mobile environment. Simulation results demonstrate the effectiveness of the proposed scheme.Comment: To appear in the Proceedings of the IEEE Global Communications Conference (GLOBECOM), Washington, DC, November 26 - 30, 200

Complete and Consistent Chiral Transport from Wigner Function Formalism

Recently there has been significant interest in understanding the macroscopic quantum transport in a many-body system of chiral fermions. A natural framework for describing such a system which is generally out of equilibrium, is the transport equation for its phase space distribution function. In this paper, we obtain a complete solution of the covariant chiral transport for massless fermions, by starting from the general Wigner function formalism and carrying out a complete and consistent semiclassical expansion up to $\hat{\mathbf{O}}(\hbar)$ order. In particular, we clarify certain subtle and confusing issues surrounding the Lorentz non-invariance and frame dependence associated with the 3D chiral kinetic theory. We prove that such frame dependence is uniquely and completely fixed by an unambiguous definition of the $\hat{\mathbf{O}}(\hbar)$ correction to the distribution function in each reference frame

Continuous-variable controlled-Z gate using an atomic ensemble

The continuous-variable controlled-Z gate is a canonical two-mode gate for universal continuous-variable quantum computation. It is considered as one of the most fundamental continuous-variable quantum gates. Here we present a scheme for realizing continuous-variable controlled-Z gate between two optical beams using an atomic ensemble. The gate is performed by simply sending the two beams propagating in two orthogonal directions twice through a spin-squeezed atomic medium. Its fidelity can run up to one if the input atomic state is infinitely squeezed. Considering the noise effects due to atomic decoherence and light losses, we show that the observed fidelities of the scheme are still quite high within presently available techniques.Comment: 7 pages, 3 figures, to appear in Physical Review