Experimental semi-device-independent certification of entangled measurements

Certifying the entanglement of quantum states with Bell inequalities allows one to guarantee the security of quantum information protocols independently of imperfections in the measuring devices. Here we present a similar procedure for witnessing entangled measurements, which play a central role in many quantum information tasks. Our procedure is termed semi-device-independent, as it uses uncharacterized quantum preparations of fixed Hilbert space dimension. Using a photonic setup, we experimentally certify an entangled measurement using measurement statistics only. We also apply our techniques to certify unentangled but nevertheless inherently quantum measurements.Comment: 7 pages, 2 figure

A Characterization of Bias Introduced into Forensic Source Identification when there is a Subpopulation Structure in the Relevant Source Population.

In forensic source identification the forensic expert is responsible for providing a summary of the evidence that allows for a decision maker to make a logical and coherent decision concerning the source of some trace evidence of interest. The academic consensus is usually that this summary should take the form of a likelihood ratio (LR) that summarizes the likelihood of the trace evidence arising under two competing propositions. These competing propositions are usually referred to as the prosecution’s proposition, that the specified source is the actual source of the trace evidence, and the defense’s proposition, that another source in a relevant background population is the actual source of the trace evidence. When a relevant background population has a subpopulation structure, the rates of misleading evidence of the LR will tend to vary within the subpopulations, sometimes to an alarming degree. Our preliminary work concerning synthetic and real data indicates that the rates of misleading evidence are different among subpopulations of different sizes, which can lead to a systematic bias when using a LR to present evidence. In this presentation we will summarize our preliminary results for characterizing this bias

Holistic juvenile justice centre: the design of a one-stop juvenile centre in Windhoek, Namibia

The promotion and protection of children's rights has since independence been a 'political commitment within the country to improve the situation of children1.Namibia has ratified the Convention on the Rights of the Child, whilst the Child Care and Protection Bill has been submitted to the Cabinet Committee on Legislation in 20102. Both seek to protect the rights of the child through a holistic approach. However, scepticism and uncertainty still pervades amongst the involved professional fields3. This can be attributed to the history of war and apartheid in Namibia, as well as social pressures of poverty and colonial legislation. Despite the adoption of national legislation respecting children's rights, difficulties in implementing the required procedural framework have placed Namibia at odds with international precedent4. In contrast, South Africa has developed specialised One-Stop Youth Justice Centres intended to promote the efficient operation of the juvenile legal system as part of promoting the rights of children5. Relying on inter-departmental cooperation, these centres are able to render comprehensive services to children in conflict with the law. Children are guided through the legal process after their arrest with the intended result of successful rehabilitation and integration into society. The main goal is to ensure that children are kept out of the conventional criminal justice system and only if rehabilitation has failed, will a child be sent to prison where a traditional sentence will be served. To better effect this these centres are to be located in residential areas. In light of international practises, courthouses are increasingly developing as specialised buildings tailored to the provision of the necessary services relevant to a particular type of civic or criminal offense6. Drawing a parallel to this, One-Stop Centres do not accommodate adult offenders, these centres are focussed on providing the necessary services to juvenile offenders and witnesses and victims of crimes committed by juveniles. This type of 'childfriendly' one-stop approach has unfortunately not permeated into the practices of the Namibian criminal justice system7. It is within this context that the design treatise has been investigated

Raman Quantum Memory with Built-In Suppression of Four-wave Mixing Noise

Quantum memories are essential for large-scale quantum information networks. Along with high efficiency, storage lifetime and optical bandwidth, it is critical that the memory add negligible noise to the recalled signal. A common source of noise in optical quantum memories is spontaneous four-wave mixing. We develop and implement a technically simple scheme to suppress this noise mechanism by means of quantum interference. Using this scheme with a Raman memory in warm atomic vapour we demonstrate over an order of magnitude improvement in noise performance. Furthermore we demonstrate a method to quantify the remaining noise contributions and present a route to enable further noise suppression. Our scheme opens the way to quantum demonstrations using a broadband memory, significantly advancing the search for scalable quantum photonic networks.Comment: 6 pages, 5 figures plus Supplementary Materia

Experimental demonstration of quantum effects in the operation of microscopic heat engines

The heat engine, a machine that extracts useful work from thermal sources, is one of the basic theoretical constructs and fundamental applications of classical thermodynamics. The classical description of a heat engine does not include coherence in its microscopic degrees of freedom. By contrast, a quantum heat engine might possess coherence between its internal states. Although the Carnot efficiency cannot be surpassed, and coherence can be performance degrading in certain conditions, it was recently predicted that even when using only thermal resources, internal coherence can enable a quantum heat engine to produce more power than any classical heat engine using the same resources. Such a power boost therefore constitutes a quantum thermodynamic signature. It has also been shown that the presence of coherence results in the thermodynamic equivalence of different quantum heat engine types, an effect with no classical counterpart. Microscopic heat machines have been recently implemented with trapped ions, and proposals for heat machines using superconducting circuits and optomechanics have been made. When operated with standard thermal baths, however, the machines implemented so far have not demonstrated any inherently quantum feature in their thermodynamic quantities. Here we implement two types of quantum heat engines by use of an ensemble of nitrogen-vacancy centres in diamond, and experimentally demonstrate both the coherence power boost and the equivalence of different heat-engine types. This constitutes the first observation of quantum thermodynamic signatures in heat machines

Ultrahigh and persistent optical depths of caesium in Kagom\'e-type hollow-core photonic crystal fibres

Alkali-filled hollow-core fibres are a promising medium for investigating light-matter interactions, especially at the single-photon level, due to the tight confinement of light and high optical depths achievable by light-induced atomic desorption. However, until now these large optical depths could only be generated for seconds at most once per day, severely limiting the practicality of the technology. Here we report the generation of highest observed transient ($>10^5$ for up to a minute) and highest observed persistent ($>2000$ for hours) optical depths of alkali vapours in a light-guiding geometry to date, using a caesium-filled Kagom\'e-type hollow-core photonic crystal fibre. Our results pave the way to light-matter interaction experiments in confined geometries requiring long operation times and large atomic number densities, such as generation of single-photon-level nonlinearities and development of single photon quantum memories.Comment: Author Accepted versio

Experimental measurement-device-independent verification of quantum steering

Bell non-locality between distant quantum systems-that is, joint correlations which violate a Bell inequality-can be verified without trusting the measurement devices used, nor those performing the measurements. This leads to unconditionally secure protocols for quantum information tasks such as cryptographic key distribution. However, complete verification of Bell non-locality requires high detection efficiencies, and is not robust to typical transmission losses over long distances. In contrast, quantum or Einstein-Podolsky-Rosen steering, a weaker form of quantum correlation, can be verified for arbitrarily low detection efficiencies and high losses. The cost is that current steering-verification protocols require complete trust in one of the measurement devices and its operator, allowing only one-sided secure key distribution. Here we present measurement-device-independent steering protocols that remove this need for trust, even when Bell non-locality is not present. We experimentally demonstrate this principle for singlet states and states that do not violate a Bell inequality.Australian Research Council/140100648Marie-Curie Fellowshi

The simplest demonstrations of quantum nonlocality

We investigate the complexity cost of demonstrating the key types of nonclassical correlations-Bell inequality violation, Einstein, Podolsky, Rosen (EPR)-steering, and entanglement-with independent agents, theoretically and in a photonic experiment. We show that the complexity cost exhibits a hierarchy among these three tasks, mirroring the recently discovered hierarchy for how robust they are to noise. For Bell inequality violations, the simplest test is the well-known Clauser-Horne-Shimony-Holt test, but for EPR-steering and entanglement the tests that involve the fewest number of detection patterns require nonprojective measurements. The simplest EPR-steering test requires a choice of projective measurement for one agent and a single nonprojective measurement for the other, while the simplest entanglement test uses just a single nonprojective measurement for each agent. In both of these cases, we derive our inequalities using the concept of circular two-designs. This leads to the interesting feature that in our photonic demonstrations, the correlation of interest is independent of the angle between the linear polarizers used by the two parties, which thus require no alignment