Operational multipartite entanglement classes for symmetric photonic qubit states

We present experimental schemes that allow to study the entanglement classes of all symmetric states in multiqubit photonic systems. In addition to comparing the presented schemes in efficiency, we will highlight the relation between the entanglement properties of symmetric Dicke states and a recently proposed entanglement scheme for atoms. In analogy to the latter, we obtain a one-to-one correspondence between well-defined sets of experimental parameters and multiqubit entanglement classes inside the symmetric subspace of the photonic system.Comment: 5 pages, 1 figur

Learning in the absence of overt practice : a novel (previously unseen) stimulus can trigger retrieval of an unpracticed response

Skilled performance is traditionally thought to develop via overt practice. Recent research has demonstrated that merely instructed stimulus-response (S-R) bindings can influence later performance and readily transfer across response modalities. In the present study, we extended this to include instructed category-response (C-R) associations. That is, we investigated whether merely instructed C-R bindings can trigger an unpracticed response (in a different modality) on perception of a novel (previously unseen) stimulus. In a learning-test design, participants had to classify stimuli by comparing them to perceptual category templates (Experiment 1) or semantic category descriptions (Experiment 2) presented prior to each block. During learning blocks, participants had to respond manually, respond vocally, or listen passively to the correct response being spoken. A manual response was always required at test. In test blocks, the categories could either be novel or repeated from the learning block, whereas half of the stimuli were always novel and half were always repeated from the learning block. Because stimulus and category repetitions were manipulated orthogonally, it was possible to directly compare the relative contribution of S-R and C-R associations to performance. In Experiment 1, test performance was enhanced by repeating the C-R bindings independently of the stimulus. In Experiment 2, there was also evidence of an S-R repetition benefit independent of the classification. Critically, instructed associations formed in one response modality were robust to changes in the required response, even when no overt response was required during training, indicating the need to update the traditional view of associative learning

Entangled-State Cycles of Atomic Collective-Spin States

We study quantum trajectories of collective atomic spin states of $N$ effective two-level atoms driven with laser and cavity fields. We show that interesting ``entangled-state cycles'' arise probabilistically when the (Raman) transition rates between the two atomic levels are set equal. For odd (even) $N$, there are $(N+1)/2$ ($N/2$) possible cycles. During each cycle the $N$-qubit state switches, with each cavity photon emission, between the states $(|N/2,m>\pm |N/2,-m>)/\sqrt{2}$, where $|N/2,m>$ is a Dicke state in a rotated collective basis. The quantum number $m$ ($>0$), which distinguishes the particular cycle, is determined by the photon counting record and varies randomly from one trajectory to the next. For even $N$ it is also possible, under the same conditions, to prepare probabilistically (but in steady state) the Dicke state $|N/2,0>$, i.e., an $N$-qubit state with $N/2$ excitations, which is of particular interest in the context of multipartite entanglement.Comment: 10 pages, 9 figure

mRNA-Expression of ERα, ERβ, and PR in Clonal Stem Cell Cultures Obtained from Human Endometrial Biopsies

Background. Proliferation and differentiation of the endometrium are regulated by estrogen and progesterone. The enormous regenerative capacity of the endometrium is thought to be based on the activity of adult stem cells. However, information on endocrine regulatory mechanisms in human endometrial stem cells is scarce. In the present study, we investigated the expression of ERα, ERβ, and PR in clonal cultures of human endometrial stem cells derived from transcervical biopsies. Methods. Endometrial tissue of 11 patients was obtained by transcervical biopsy. Stromal cell suspensions were plated at clonal density and incubated for 15 days. Expression of ERα, ERβ and PR was determined by qPCR prior to and after one cloning round, and normalized to 18 S rRNA expression. Results. Expression of ERα and ERβ was downregulated by 64% and 89%, respectively (P = 0.002 and P < 0.001). In contrast, PR was not significantly downregulated, due to a more heterogenous expression pattern. Conclusions. Culture of human endometrial stroma cells results in a downregulation of ERα and ERβ, while expression of PR remained unchanged in our patient collective. These results support the hypothesis that stem cells may not be subject to direct stimulation by sex steroids, but rather by paracrine mechanisms within the stem cell niche

Realization of a Knill-Laflamme-Milburn C-NOT gate -a photonic quantum circuit combining effective optical nonlinearities

Quantum information science addresses how uniquely quantum mechanical phenomena such as superposition and entanglement can enhance communication, information processing and precision measurement. Photons are appealing for their low noise, light-speed transmission and ease of manipulation using conventional optical components. However, the lack of highly efficient optical Kerr nonlinearities at single photon level was a major obstacle. In a breakthrough, Knill, Laflamme and Milburn (KLM) showed that such an efficient nonlinearity can be achieved using only linear optical elements, auxiliary photons, and measurement. They proposed a heralded controlled-NOT (CNOT) gate for scalable quantum computation using a photonic quantum circuit to combine two such nonlinear elements. Here we experimentally demonstrate a KLM CNOT gate. We developed a stable architecture to realize the required four-photon network of nested multiple interferometers based on a displaced-Sagnac interferometer and several partially polarizing beamsplitters. This result confirms the first step in the KLM `recipe' for all-optical quantum computation, and should be useful for on-demand entanglement generation and purification. Optical quantum circuits combining giant optical nonlinearities may find wide applications across telecommunications and sensing.Comment: 6pages, 3figure

Request-a-bet sports betting products indicate patterns of bettor preference and bookmaker profits

Background and aims Request-a-bet services are a modern gambling product delivered via the social network Twitter, which allow sports bettors to design custom bets. The public nature of Twitter data provided a unique opportunity to investigate patterns of bettor preference and the bookmaker profit margin in soccer, the UK’s favorite sport. Methods Two multi-method studies. Twitter users’ engagement with request-a-bet services was monitored unobtrusively (n = 1,406), meaning that potential patterns across users’ requests could be observed, and the bookmaker profit margin could be estimated. Twitter users were also surveyed directly (n = 55), providing self-report measures of request-a-bet usage. Results Twitter users requested bets with an average potential payoff of £56.5 per £1 risked (median = £9). Overall, 9.7% of requested bets paid-off, but these were mostly bets at short odds. This meant that requests yielded a high bookmaker profit margin of 43.7% (roughly eight times higher than current margins in conventional soccer bets), which increased to 74.6% for bets at longer odds. Requested bets also tended to involve star players from the best teams. Finally, 92.7% of surveyed Twitter users reported placing at least one bet via request-a-bet services (mean = 44.4 bets). Discussion and conclusions Researchers can use request-a-bet products to increase their understanding of sports betting behavior. Sports bettors should be given information about how much higher the bookmaker profit margin can be in modern sports bets compared to the conventional sports bets that they may be more familiar with

Experimental entanglement of a six-photon symmetric Dicke state

We report on the experimental observation and characterization of a six-photon entangled Dicke state. We obtain a fidelity as high as 0.654$\pm$0.024 and prove genuine six-photon entanglement by, amongst others, a two-setting witness yielding -0.422$\pm$0.148. This state has remarkable properties; e.g., it allows obtaining inequivalent entangled states of a lower qubit number via projective measurements, and it possesses a high entanglement persistency against qubit loss. We characterize the properties of the six-photon Dicke state experimentally by detecting and analyzing the entanglement of a variety of multipartite entangled states.Comment: replaced with published versio

A simple scheme for expanding photonic cluster states for quantum information

We show how an entangled cluster state encoded in the polarization of single photons can be straightforwardly expanded by deterministically entangling additional qubits encoded in the path degree of freedom of the constituent photons. This can be achieved using a polarization--path controlled-phase gate. We experimentally demonstrate a practical and stable realization of this approach by using a Sagnac interferometer to entangle a path qubit and polarization qubit on a single photon. We demonstrate precise control over phase of the path qubit to change the measurement basis and experimentally demonstrate properties of measurement-based quantum computing using a 2 photon, 3 qubit cluster state