Extracting joint weak values with local, single-particle measurements

Weak measurement is a new technique which allows one to describe the evolution of postselected quantum systems. It appears to be useful for resolving a variety of thorny quantum paradoxes, particularly when used to study properties of pairs of particles. Unfortunately, such nonlocal or joint observables often prove difficult to measure weakly in practice (for instance, in optics -- a common testing ground for this technique -- strong photon-photon interactions would be needed). Here we derive a general, experimentally feasible, method for extracting these values from correlations between single-particle observables.Comment: 6 page

Inhibition of Food Intake by PACAP in the Hypothalamic Ventromedial Nuclei is Mediated by NMDA Receptors

Central injections of pituitary adenylate cyclase-activating polypeptide (PACAP) into the ventromedial nuclei (VMN) of the hypothalamus produce hypophagia that is dependent upon the PAC1 receptor; however, the signaling downstream of this receptor in the VMN is unknown. Though PACAP signaling has many targets, this neuropeptide has been shown to influence glutamate signaling in several brain regions through mechanisms involving NMDA receptor potentiation via activation of the Src family of protein tyrosine kinases. With this in mind, we examined the Src-NMDA receptor signaling pathway as a target for PACAP signaling in the VMN that may mediate its effects on feeding behavior. Under nocturnal feeding conditions, NMDA receptor antagonism prior to PACAP administration into the VMN attenuated PACAP-mediated decreases in feeding suggesting that glutamatergic signaling via NMDA receptors is necessary for PACAP-induced hypophagia. Furthermore, PACAP administration into the VMN resulted in increased tyrosine phosphorylation of the GluN2B subunit of the NMDA receptor, and inhibition of Src kinase activity also blocked the effects of PACAP administration into the VMN on feeding behavior. These results indicate that PACAP neurotransmission in the VMN likely augments glutamate signaling by potentiating NMDA receptors activity through the tyrosine phosphorylation events mediated by the Src kinase family, and modulation of NMDA receptor activity by PACAP in the hypothalamus may be a primary mechanism for its regulation of food intake

Spatio-Temporal Sentiment Hotspot Detection Using Geotagged Photos

We perform spatio-temporal analysis of public sentiment using geotagged photo collections. We develop a deep learning-based classifier that predicts the emotion conveyed by an image. This allows us to associate sentiment with place. We perform spatial hotspot detection and show that different emotions have distinct spatial distributions that match expectations. We also perform temporal analysis using the capture time of the photos. Our spatio-temporal hotspot detection correctly identifies emerging concentrations of specific emotions and year-by-year analyses of select locations show there are strong temporal correlations between the predicted emotions and known events.Comment: To appear in ACM SIGSPATIAL 201

Comment on "A linear optics implementation of weak values in Hardy's paradox"

A recent experimental proposal by Ahnert and Payne [S.E. Ahnert and M.C. Payne, Phys. Rev. A 70, 042102 (2004)] outlines a method to measure the weak value predictions of Aharonov in Hardy's paradox. This proposal contains flaws such as the state preparation method and the procedure for carrying out the requisite weak measurements. We identify previously published solutions to some of the flaws.Comment: To be published in Physical Review

Experimental bound entanglement in a four-photon state

Entanglement [1, 2] enables powerful new quantum technologies [3-8], but in real-world implementations, entangled states are often subject to decoherence and preparation errors. Entanglement distillation [9, 10] can often counteract these effects by converting imperfectly entangled states into a smaller number of maximally entangled states. States that are entangled but cannot be distilled are called bound entangled [11]. Bound entanglement is central to many exciting theoretical results in quantum information processing [12-14], but has thus far not been experimentally realized. A recent claim for experimental bound entanglement is not supported by their data [15]. Here, we consider a family of four-qubit Smolin states [16], focusing on a regime where the bound entanglement is experimentally robust. We encode the state into the polarization of four photons and show that our state exhibits both entanglement and undistillability, the two defining properties of bound entanglement. We then use our state to implement entanglement unlocking, a key feature of Smolin states [16].Comment: 10 pages, 6 figures. For a simultaneously submitted related work see arXiv:1005.196

Full characterization of a three-photon GHZ state using quantum state tomography

We have performed the first experimental tomographic reconstruction of a three-photon polarization state. Quantum state tomography is a powerful tool for fully describing the density matrix of a quantum system. We measured 64 three-photon polarization correlations and used a "maximum-likelihood" reconstruction method to reconstruct the GHZ state. The entanglement class has been characterized using an entanglement witness operator and the maximum predicted values for the Mermin inequality was extracted.Comment: 3 pages, 3 figure

\u3cem\u3eN\u3c/em\u3e-acetylcysteine Decreases Binge Eating in a Rodent Model

Binge-eating behavior involves rapid consumption of highly palatable foods leading to increased weight gain. Feeding in binge disorders resembles other compulsive behaviors, many of which are responsive to N-acetylcysteine (NAC), which is a cysteine prodrug often used to promote non-vesicular glutamate release by a cystine–glutamate antiporter. To examine the potential for NAC to alter a form of compulsive eating, we examined the impact of NAC on binge eating in a rodent model. Specifically, we monitored consumption of standard chow and a high-fat, high carbohydrate western diet (WD) in a rodent limited-access binge paradigm. Before each session, rats received either a systemic or intraventricular injection of NAC. Both systemic and central administration of NAC resulted in significant reductions of binge eating the WD without decreasing standard chow consumption. The reduction in WD was not attributable to general malaise as NAC did not produce condition taste aversion. These results are consistent with the clinical evidence of NAC to reduce or reverse compulsive behaviors, such as, drug addiction, skin picking and hair pulling

Manipulating biphotonic qutrits

Quantum information carriers with higher dimension than the canonical qubit offer significant advantages. However, manipulating such systems is extremely difficult. We show how measurement induced non-linearities can be employed to dramatically extend the range of possible transforms on biphotonic qutrits; the three level quantum systems formed by the polarisation of two photons in the same spatio-temporal mode. We fully characterise the biphoton-photon entanglement that underpins our technique, thereby realising the first instance of qubit-qutrit entanglement. We discuss an extension of our technique to generate qutrit-qutrit entanglement and to manipulate any bosonic encoding of quantum information.Comment: 4 pages, 4 figure

A conditional-phase switch at the single-photon level

We present an experimental realization of a two-photon conditional-phase switch, related to the ``$c$-$\phi$'' gate of quantum computation. This gate relies on quantum interference between photon pairs, generating entanglement between two optical modes through the process of spontaneous parametric down-conversion (SPDC). The interference effect serves to enhance the effective nonlinearity by many orders of magnitude, so it is significant at the quantum (single-photon) level. By adjusting the relative optical phase between the classical pump for SPDC and the pair of input modes, one can impress a large phase shift on one beam which depends on the presence or absence of a single photon in a control mode.Comment: 8 pages, 4 figure