Frequency-Bin Entanglement of Ultra-Narrow Band Non-Degenerate Photon Pairs

We demonstrate frequency-bin entanglement between ultra-narrowband photons generated by cavity enhanced spontaneous parametric down conversion. Our source generates photon pairs in widely non-degenerate discrete frequency modes, with one photon resonant with a quantum memory material based on praseodymium doped crystals and the other photon at telecom wavelengths. Correlations between the frequency modes are analyzed using phase modulators and narrowband filters before detection. We show high-visibility two photon interference between the frequency modes, allowing us to infer a coherent superposition of the modes. We develop a model describing the state that we create and use it to estimate optimal measurements to achieve a violation of the Clauser-Horne (CH) Bell inequality under realistic assumptions. With these settings we perform a Bell test and show a significant violation of the CH inequality, thus proving the entanglement of the photons. Finally we demonstrate the compatibility with a quantum memory material by using a spectral hole in the praseodymium (Pr) doped crystal as spectral filter for measuring high-visibility two-photon interference. This demonstrates the feasibility of combining frequency-bin entangled photon pairs with Pr-based solid state quantum memories.Comment: 15 pages, 6 figure

Visible-to-telecom quantum frequency conversion of light from a single quantum emitter

Quantum frequency conversion (QFC), a nonlinear optical process in which the frequency of a quantum light field is altered while conserving its non-classical correlations, was first demonstrated 20 years ago. Meanwhile, it is considered an essential tool for the implementation of quantum repeaters since it allows for interfacing quantum memories with telecom-wavelength photons as quantum information carriers. Here we demonstrate efficient (>30%) QFC of visible single photons (711 nm) emitted by a quantum dot (QD) to a telecom wavelength (1,313 nm). Analysis of the first and second-order coherence before and after wavelength conversion clearly proves that important properties, such as the coherence time and photon antibunching, are fully conserved during the frequency translation process. Our findings underline the great potential of single photon sources on demand in combination with QFC as a promising technique for quantum repeater schemes.Comment: 11 pages, 4 figure

Regeneration in starved planarians depends on TRiC/CCT subunits modulating the unfolded protein response

Planarians are able to stand long periods of starvation by maintaining adult stem cell pools and regenerative capacity. The molecular pathways that are needed for the maintenance of regeneration during starvation are not known. Here, we show that down‐regulation of chaperonin TRiC/CCT subunits abrogates the regeneration capacity of planarians during starvation, but TRiC/CCT subunits are dispensable for regeneration in fed planarians. Under starvation, they are required to maintain mitotic fidelity and for blastema formation. We show that TRiC subunits modulate the unfolded protein response (UPR) and are required to maintain ATP levels in starved planarians. Regenerative defects in starved CCT‐depleted planarians can be rescued by either chemical induction of mild endoplasmic reticulum stress, which leads to induction of the UPR, or by the supplementation of fatty acids. Together, these results indicate that CCT‐dependent UPR induction promotes regeneration of planarians under food restriction

Tnfaip2/exoc3 ‐driven lipid metabolism is essential for stem cell differentiation and organ homeostasis

Abstract Lipid metabolism influences stem cell maintenance and differentiation but genetic factors that control these processes remain to be delineated. Here, we identify Tnfaip2 as an inhibitor of reprogramming of mouse fibroblasts into induced pluripotent stem cells. Tnfaip2 knockout impairs differentiation of embryonic stem cells (ESCs), and knockdown of the planarian para‐ortholog, Smed‐exoc3 , abrogates in vivo tissue homeostasis and regeneration—processes that are driven by somatic stem cells. When stimulated to differentiate, Tnfaip2 ‐deficient ESCs fail to induce synthesis of cellular triacylglycerol (TAG) and lipid droplets (LD) coinciding with reduced expression of vimentin ( Vim )—a known inducer of LD formation. Smed‐exoc3 depletion also causes a strong reduction of TAGs in planarians. The study shows that Tnfaip2 acts epistatically with and upstream of Vim in impairing cellular reprogramming. Supplementing palmitic acid (PA) and palmitoyl‐L‐carnitine (the mobilized form of PA) restores the differentiation capacity of Tnfaip2 ‐deficient ESCs and organ maintenance in Smed‐exoc3 ‐depleted planarians. Together, these results identify a novel role of Tnfaip2 and exoc3 in controlling lipid metabolism, which is essential for ESC differentiation and planarian organ maintenance