Characterization of tomographically faithful states in terms of their Wigner function

Joint measurement of complementary observables in moment tomography

Wigner and Husimi quasi-distributions, owing to their functional regularity, give the two archetypal and equivalent representations of all observable-parameters in continuous-variable quantum information. Balanced homodyning and heterodyning that correspond to their associated sampling procedures, on the other hand, fare very differently concerning their state or parameter reconstruction accuracies. We present a general theory of a now-known fact that heterodyning can be tomographically more powerful than balanced homodyning to many interesting classes of single-mode quantum states, and discus…

Local sampling of the SU(1,1) Wigner function

Despite the indisputable merits of the Wigner phase-space formulation, it has not been widely explored for systems with SU(1,1) symmetry, as a simple operational definition of the Wigner function has proved elusive in this case. We capitalize on the unique properties of the parity operator, to derive in a consistent way a \emph{bona fide} SU(1,1) Wigner function that faithfully parallels the structure of its continuous-variable counterpart. We propose an optical scheme, involving a squeezer and photon-number-resolving detectors, that allows for direct point-by-point sampling of that Wigner fun…

Teleportation fidelity as a probe of sub-Planck phase-space structure

We investigate the connection between sub-Planck structure in the Wigner function and the output fidelity of continuous-variable teleportation protocols. When the teleporting parties share a two-mode squeezed state as an entangled resource, high fidelity in the output state requires a squeezing large enough that the smallest sub-Planck structures in an input pure state are teleported faithfully. We formulate this relationship, which leads to an explicit relation between the fine-scale structure in the Wigner function and large-scale extent of the Wigner function, and we treat specific examples…

Self assembled Wigner crystals as mediators of spin currents and quantum information

Technological applications of many-body structures that emerge in gated devices under minimal control are largely unexplored. Here we show how emergent Wigner crystals in a semiconductor quantum wire can facilitate a pivotal requirement for a scalable quantum computer, namely transmitting quantum information encoded in spins faithfully over a distance of micrometers. The fidelity of the transmission is remarkably high, faster than the relevant decohering effects, independent of the details of the spatial charge configuration in the wire, and realizable in dilution refrigerator temperatures. Th…

探索用于光量子态的复值非高斯性度量的可能性

Exploring the possibility of a complex-valued non-Gaussianity measure for quantum states of light

本文提出一种基于相空间的复值非高斯性度量，即 Wigner 函数与其高斯伴随函数间的微分相对熵，证明其具有忠实性、高斯酉不变性及高斯信道单调性，其实部提供额外信息，虚部对应 Wigner 函数负体积，并验证了其在非高斯量子态工程中的实用性。

量子签名与塞曼极限在福克态传输中的表现

Quantum signatures and semiclassical limitations in the transmission of Fock states

本文研究了福克态通过倒置振子势垒的传输，探讨了经典方法在捕捉量子干涉方面的局限性，并指出塞曼方法无法描述Wigner函数负性带来的短时间平台效应。