Effect of Polarization Dependent Loss on the Quality of Transmitted Polarization Entanglement

Abstract

Quantum networking brings together several diverse research areas, such as fiber-optic communication, quantum optics, and quantum information, to achieve capabilities in security, secret sharing, and authentication which are unavailable classically. The development of practical fiber-based quantum networks requires an understanding of the reach, rates, and quality of the entanglement of distributed quantum states. Here, we present a theoretical model describing how the magnitude and orientation of polarization dependent loss (PDL), a common impairment in fiber-optic networks, affects the entanglement quality of distributed quantum states. Furthermore, we theoretically characterize how PDL in one fiber channel can be optimally applied in order to nonlocally compensate for the PDL present in another channel. We present experimental results that verify our theoretical model. Index Terms-Optical fiber communication, quantum entanglement. I. INTRODUCTION Q UANTUM networks promise to offer functionalities unavailable classically by using distributed quantum entanglement as a resource [1]. Essential to the development of a quantum network is the ability to create, manipulate, and distribute entanglement between distant nodes [2]. It would be desirable to leverage the vast deployed fiber optics infrastructure for entanglement distribution. However, entanglement is fragile, and a greater understanding of how transmission through fibers and fiber components affects entanglement quality is required in order to successfully develop a fiber-based quantum network. Specifically, for the distribution of polarization-entangled states, polarization mode dispersion (PMD) and polarization dependent loss (PDL) are the two principal effects which must be accounted for [3]-[5]. While the PDL of the fibers itself is often low, PDL is commonly found in optical components, such as isolators, multiplexers, and couplers, where the attenuations of the two orthogonal polarization modes can differ. The effects of PDL in classical communication have been thoroughly investigated over the

Exploring classical correlations in noise to recover quantum information using local filtering

“…This was done so that the theoretical mutual information agreed with the average mutual information of the density matrices measured with γ A = 0 and γ B = 0. Note that a similar normalization factor of 0.925 was necessary when characterizing the concurrence of a similar entangled photon source in our previous work [24,25]. We speculate that the additional normalization was required in each experiment due to some unaccounted noise such as Raman scattered photons and/or leakage from the pump.…”

“…Our results offer tantalizing hope for error-free quantum information transmission in the future. Here, we expand on our recent theoretical results [25] to derive the magnitude of the filter γ B that produces maximum entanglement. Both states ρ bf and ρ pf are Bell diagonal states [46] and can therefore be expressed, up to local unitary rotations, as:…”

“…Both noise terms N bf and N pf are rank-2 Bell diagonal states. Compared to the isotropic rank-4 noise theoretically considered previously for Werner states [25], the terms N bf and N pf represent more realistic scenarios. The properties of the two are drastically different, however.…”

Entanglement Robustness in Trace Decreasing Quantum Dynamics

“…The effect of polarization dependent losses is that the states with different polarization are attenuated differently [16,17,34,35]. Let the horizontally and vertically polarized states be those that are the least and most attenuated, or vice versa.…”

“…In addition to a general result, in Section 3, we elaborate the case of polarization dependent losses accompanied by depolarization. This model of loss and noise describes effects in some optical fibers and attracts increasing attention in the literature [34,35]. In this model, each Λ i (t) is defined by three parameters: the depolarization rate γ and the attenuation coefficients for horizontally and vertically polarized photons, γ H and γ V .…”