Distillation of Quantum Steering.

We show-both theoretically and experimentally-that Einstein-Podolsky-Rosen steering can be distilled. We present a distillation protocol that outputs a perfectly correlated system-the singlet assemblage-in the asymptotic infinite-copy limit, even for inputs that are arbitrarily close to being unsteerable. As figures of merit for the protocol's performance, we introduce the assemblage fidelity and the singlet-assemblage fraction. These are potentially interesting quantities on their own beyond the current scope. Remarkably, the protocol works well also in the nonasymptotic regime of few copies, in the sense of increasing the singlet-assemblage fraction. We demonstrate the efficacy of the protocol using a hyperentangled photon pair encoding two copies of a two-qubit state. This represents to our knowledge the first observation of deterministic steering concentration. Our findings are not only fundamentally important but may also be useful for semi-device-independent protocols in noisy quantum networks.

Heralded Single Photons Based on Spectral Multiplexing and Feed-Forward Control.

We propose and experimentally demonstrate a novel approach to a heralded single-photon source based on spectral multiplexing (SMUX) and feed-forward-based spectral manipulation of photons created by means of spontaneous parametric down-conversion in a periodically poled LiNbO_{3} crystal. As a proof of principle, we show that our three-mode SMUX increases the heralded single-photon rate compared to that of the individual modes without compromising the quality of the emitted single photons. We project that by adding further modes, our approach can lead to a deterministic single-photon source.

Experimental entanglement redistribution under decoherence channels.

When an initially entangled pair of qubits undergoes local decoherence processes, there are a number of ways in which the original entanglement can spread throughout the multipartite system consisting of the two qubits and their environments. Here, we report theoretical and experimental results regarding the dynamics of the distribution of entanglement in this system. The experiment employs an all optical setup in which the qubits are encoded in the polarization degrees of freedom of two photons, and each local decoherence channel is implemented with an interferometer that couples the polarization to the path of each photon, which acts as an environment. We monitor the dynamics and distribution of entanglement and observe the transition from bipartite to multipartite entanglement and back, and show how these transitions are intimately related to the sudden death and sudden birth of entanglement. The multipartite entanglement is further analyzed in terms of three- and four-partite entanglement contributions, and genuine four-qubit entanglement is observed at some points of the evolution.

Linear-optical simulation of the cooling of a cluster-state Hamiltonian system.

A measurement-based quantum computer could consist of a local-gapped Hamiltonian system, whose thermal states-at sufficiently low temperature-are universal resources for the computation. Initialization of the computer would correspond to cooling the system. We perform an experimental quantum simulation of such a cooling process with entangled photons. We prepare three-qubit thermal cluster states exploiting the equivalence between local dephasing and thermalization for these states. This allows us to tune the system's temperature by changing the dephasing strength. We monitor the entanglement as the system cools down and observe the transitions from separability to bound entanglement, and then to free entanglement. We also analyze the performance of the system for measurement-based single-qubit state preparation. These studies constitute a basic characterization of experimental cluster-state computation under imperfect conditions.

Experimental estimate of a classicality witness via a single measurement.

The perception that quantum correlations can still appear in separable states has opened exciting new possibilities regarding their use as a resource in quantum information science. Quantifying such quantum correlations involves the complete knowledge of the system's state and numerical optimization procedures. Thus, it is natural to seek methods involving fewer measurements that indicate the nature of the correlations in a system. Here we propose a classicality witness that can be accurately estimated via statistics from a single measurement and perform an experiment to explore the utility of this witness for quantum states with different types of correlations.

Observation of the emergence of multipartite entanglement between a bipartite system and its environment.

The dynamics of the environment is usually experimentally inaccessible and hence ignored for open systems. Here we overcome this limitation by using an interferometric setup that allows the implementation of several decoherence channels and full access to all environmental degrees of freedom. We show that when a qubit from an entangled pair interacts with the environment, the initial bipartite entanglement gets redistributed into bipartite and genuine multipartite entanglements involving the two qubits and the environment. This is yet another trait of the subtle behavior of entangled open systems.

Emergence of the pointer basis through the dynamics of correlations.

We use the classical correlation between a quantum system being measured and its measurement apparatus to analyze the amount of information being retrieved in a quantum measurement process. Accounting for decoherence of the apparatus, we show that these correlations may have a sudden transition from a decay regime to a constant level. This transition characterizes a nonasymptotic emergence of the pointer basis, while the system apparatus can still be quantum correlated. We provide a formalization of the concept of emergence of a pointer basis in an apparatus subject to decoherence. This contrast of the pointer basis emergence to the quantum to classical transition is demonstrated in an experiment with polarization entangled photon pairs.

Entanglement between more than two hundred macroscopic atomic ensembles in a solid.

There are both fundamental and practical motivations for studying whether quantum entanglement can exist in macroscopic systems. However, multiparty entanglement is generally fragile and difficult to quantify. Dicke states are multiparty entangled states where a single excitation is delocalized over many systems. Building on previous work on quantum memories for photons, we create a Dicke state in a solid by storing a single photon in a crystal that contains many large atomic ensembles with distinct resonance frequencies. The photon is re-emitted at a well-defined time due to an interference effect analogous to multi-slit diffraction. We derive a lower bound for the number of entangled ensembles based on the contrast of the interference and the single-photon character of the input, and we experimentally demonstrate entanglement between over two hundred ensembles, each containing a billion atoms. We also illustrate the fact that each individual ensemble contains further entanglement.Multipartite entanglement is of both fundamental and practical interest, but is notoriously difficult to witness and characterise. Here, Zarkeshian et al. demonstrate multipartite entanglement in an atomic frequency comb storing a single photon in a Dicke state spread over a macroscopic ensemble.

Detection of entanglement in asymmetric quantum networks and multipartite quantum steering.

The future of quantum communication relies on quantum networks composed by observers sharing multipartite quantum states. The certification of multipartite entanglement will be crucial to the usefulness of these networks. In many real situations it is natural to assume that some observers are more trusted than others in the sense that they have more knowledge of their measurement apparatuses. Here we propose a general method to certify all kinds of multipartite entanglement in this asymmetric scenario and experimentally demonstrate it in an optical experiment. Our results, which can be seen as a definition of genuine multipartite quantum steering, give a method to detect entanglement in a scenario in between the standard entanglement and fully device-independent scenarios, and provide a basis for semi-device-independent cryptographic applications in quantum networks.

Ecological constraints drive social evolution in the African mole-rats.

The African mole-rats (family Bathyergidae) are subterranean hystricomorph rodents occurring in a variety of habitats and displaying levels of sociality which range from solitary to eusocial, making them a unique mammalian taxonomic group to test ecological influences on sociality. Here, we use an extensive DNA-based phylogeny and comparative analysis to investigate the relationship between ecology, sociality and evolution within the family. Mitochondrial cytochrome-b and 12s rRNA trees reveal that the solitary species are monophyletic when compared to the social species. The naked mole-rat (Heterocephalus glaber) is ancestral and divergent from the Damaraland mole-rat (Cryptomys damarensis), supporting previous findings that have suggested the multiple evolution of eusociality within the family. The Cryptomys genus is species-rich and contains taxa exhibiting different levels of sociality, which can be divided into two distinct clades. A total of seven independent comparisons were generated within the phylogeny, and three ecological variables were significantly correlated with social group size: geophyte density (p < 0.05), mean months per year of rainfall greater than 25 mm (p < 0.001), and the coefficient of rainfall variation (p = 0.001). These results support the food-aridity hypothesis for the evolution of highly social cooperative behaviour in the Bathyergidae, and are consistent with the current theoretical framework for skew theory.

Thermoregulation in three species of Afrotropical subterranean mole-rats (Rodentia: Bathyergidae) from Zambia and Angola and scaling within the genus Cryptomys.

The thermoregulatory characteristics of three species of Cryptomys from Zambia and Angola are examined and, together with published data on four other species of Cryptomys from southern Africa, used to determine whether scaling occurs in this genus of subterranean rodents. The thermoregulatory properties of acclimated giant Zambian mole-rats, Cryptomys mechowi ([Formula: see text]=267 g), Angolan mole-rats, Cryptomys bocagei ([Formula: see text]=94 g) and Zambian common mole-rats Cryptomys hottentotus amatus ([Formula: see text]=77 g) are as follows. Mean resting metabolic rates (RMRs) within the respective thermoneutral zones were 0.60±0.08 cm3 O2 g-1 h-1 (n=12) for C. mechowi; 0.74±0.06 cm3 O2 g-1 h-1 (n=8) for C. bocagei and 0.63±0.06 cm3O2 g-1 h-1 (n=21) for C. h. amatus. The thermoneutral zones (TNZs) of all three species are narrow: 29-30°C for C. mechowi; 31.5-32.5°C for C. bocagei and 28-32° C for C. h. amatus. The increase in mean RMR at the lowest temperatures tested (15° C for C. mechowi, 18° C for C. bocagei and C. h. amatus) was 2.35, 2.2 and 3.82 times their RMR in the TNZ respectively. Body temperatures are low, 34±0.53° C (n=24) for C. mechowi, 33.7±0.32° C (n=20) for C. bocagei and 33.8±0.43° C (n=40) for C. h amatus. At the lower limit of thermoneutrality, conductances are 0.09±0.01 cm3 O2 g-1 h-1 °C-1 (n=30) in C. mechowi; 0.12±0.01 cm3 O2 g-1 h-1 °C-1 (n=20) in C. bocagei and 0.12±0.03 cm3 O2 g-1 h-1 °C-1 (n=32) in C. h. amatus. The range in mean body mass among the seven species of Cryptomys examined for scaling was 60 g (C. darlingi) to 267 g (C. mechowi). There is no clear relationship between RMR within the TNZ and body mass. The resultant relationship is represented by the power curve RMR=2.45 mass-0.259.