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A. Martin

Publications and source records attributed to A. Martin.

At least 55 records · Page 3Linked to original sources
arXiv2015

Resource-efficient measurement device independent entanglement witness

Imperfections in experimental measurement schemes can lead to falsely identifying, or over estimating, entanglement in a quantum system. A recent solution to this is to define schemes that are robust to measurement imperfections - measurement device independent entanglement witness (MDI-EW). Here we introduce a novel approach for MDI-EW, which significantly reduces the experimental complexity and is applicable to a wide range of physical systems. The scheme requires no prior description of the state, is detection loop-hole free, robust to classical communication, and works for all entangled qubit states. We focus on photonic entanglement, experimentally generating and testing bipartite Werner states, varying the entanglement from the maximally entangled Bell state, past the bound for nonlocal states and down to the separable bound of 1/3. We witness entanglement down to an entangled state fraction close to 0.4. These results could be of particular interest for device independent quantum random number generation.

quant-ph↗
arXiv2015

Quantum random number generation for 1.25 GHz quantum key distribution systems

Security proofs of quantum key distribution (QKD) systems usually assume that the users have access to source of perfect randomness. State-of-the-art QKD systems run at frequencies in the GHz range, requiring a sustained GHz rate of generation and acquisition of quantum random numbers. In this paper we demonstrate such a high speed random number generator. The entropy source is based on amplified spontaneous emission from an erbium-doped fibre, which is directly acquired using a standard small form-factor pluggable (SFP) module. The module connects to the Field Programmable Gate Array (FPGA) of a QKD system. A real-time randomness extractor is implemented in the FPGA and achieves a sustained rate of 1.25 Gbps of provably random bits.

quant-ph↗
arXiv2015

Dirac Triplet Extension of the MSSM

In this paper we explore extensions of the Minimal Supersymmetric Standard Model involving two $SU(2)_L$ triplet chiral superfields that share a superpotential Dirac mass yet only one of which couples to the Higgs fields. This choice is motivated by recent work using two singlet superfields with the same superpotential requirements. We find that, as in the singlet case, the Higgs mass in the triplet extension can easily be raised to $125\,\text{GeV}$ without introducing large fine-tuning. For triplets that carry hypercharge, the regions of least fine tuning are characterized by small contributions to the $\mathcal T$ parameter, and light stop squarks, $m_{\tilde t_1} \sim 300-450\,\text{GeV}$; the latter is a result of the $\tanβ$ dependence of the triplet contribution to the Higgs mass. Despite such light stop masses, these models are viable provided the stop-electroweakino spectrum is sufficiently compressed.

hep-ph↗
arXiv2015

Comparing different approaches for generating random numbers device-independently using a photon pair source

What is the most efficient way to generate random numbers device-independently using a photon pair source based on spontaneous parametric down conversion (SPDC)? We consider this question by comparing two implementations of a detection-loophole-free Bell test. In particular, we study in detail a scenario where a heralded single photon source (HSPS) is used to herald path-entangled states, i.e. entanglement between two spatial modes sharing a single photon and where non-locality is revealed using photon counting preceded by small displacement operations. We start by giving a theoretical description of such a measurement. We then show how to optimize the Bell-CHSH violation through a non-perturbative calculation, taking the main experimental imperfections into account. We finally bound the amount of randomness that can be extracted and compare it to the one obtained with the conventional scenario using photon pairs entangled e.g. in polarization and analyzed through photon counting. While the former requires higher overall detection efficiencies, it is far more efficient in terms of both the entropy per experimental run and the rate of random bit generation.

quant-ph↗
arXiv2015

Revealing Genuine Optical-Path Entanglement

How can one detect entanglement between multiple optical paths sharing a single photon? We address this question by proposing a scalable protocol, which only uses local measurements where single photon detection is combined with small displacement operations. The resulting entanglement witness does not require post-selection, nor assumptions about the photon number in each path. Furthermore, it guarantees that entanglement lies in a subspace with at most one photon per optical path and reveals genuinely multipartite entanglement. We demonstrate its scalability and resistance to loss by performing various experiments with two and three optical paths. We anticipate applications of our results for quantum network certification.

quant-ph↗
arXiv2014

Breaking Points in Quartic Maps

Dynamical systems, whether continuous or discrete, are used by physicists in order to study non-linear phenomena. In the case of discrete dynamical systems, one of the most used is the quadratic map depending on a parameter. However, some phenomena can depend alternatively of two values of the same parameter. We use the quadratic map $x_{n+1} =1-ax_{n}^{2} $ when the parameter alternates between two values during the iteration process. In this case, the orbit of the alternate system is the sum of the orbits of two quartic maps. The bifurcation diagrams of these maps present breaking points where abruptly change their evolution.

nlin.CD↗
arXiv2014

Challenging preconceptions about Bell tests with photon pairs

Motivated by very recent experiments, we consider a scenario "à la Bell" in which two protagonists test the Clauser-Horne-Shimony-Holt (CHSH) inequality using a photon-pair source based on spontaneous parametric down conversion and imperfect photon detectors. The conventional wisdom says that (i) if the detectors have unit efficiency, the CHSH violation can reach its maximum quantum value $2\sqrt{2}$. To obtain the maximal possible violation, it suffices that the source emits (ii) maximally entangled photon pairs (iii) in two well defined single modes. Through a non-perturabive calculation of non-local correlations, we show that none of these statements are true. By providing the optimal pump parameters, measurement settings and state structure for any detection efficiency and dark count probability, our results give the recipe to close all the loopholes in a Bell test using photon pairs.

quant-ph↗
arXiv2014

Polarization entangled photon-pair source based on quantum nonlinear photonics and interferometry

We present a versatile, high-brightness, guided-wave source of polarization entangled photons, emitted at a telecom wavelength. Photon-pairs are generated using an integrated type-0 nonlinear waveguide, and subsequently prepared in a polarization entangled state via a stabilized fiber interferometer. We show that the single photon emission wavelength can be tuned over more than 50 nm, whereas the single photon spectral bandwidth can be chosen at will over more than five orders of magnitude (from 25 MHz to 4 THz). Moreover, by performing entanglement analysis, we demonstrate a high degree of control of the quantum state via the violation of the Bell inequalities by more than 40 standard deviations. This makes this scheme suitable for a wide range of quantum optics experiments, ranging from fundamental research to quantum information applications. We report on details of the setup, as well as on the characterization of all included components, previously outlined in F. Kaiser et al. (2013 Laser Phys. Lett. 10, 045202).

quant-ph↗
arXiv2014

Nonlinear interaction between two heralded single photons

Harnessing nonlinearities strong enough to allow two single photons to interact with one another is not only a fascinating challenge but is central to numerous advanced applications in quantum information science. Currently, all known approaches are extremely challenging although a few have led to experimental realisations with attenuated classical laser light. This has included cross-phase modulation with weak classical light in atomic ensembles and optical fibres, converting incident laser light into a non-classical stream of photon or Rydberg blockades as well as all-optical switches with attenuated classical light in various atomic systems. Here we report the observation of a nonlinear parametric interaction between two true single photons. Single photons are initially generated by heralding one photon from each of two independent spontaneous parametric downconversion sources. The two heralded single photons are subsequently combined in a nonlinear waveguide where they are converted into a single photon with a higher energy. Our approach highlights the potential for quantum nonlinear optics with integrated devices, and as the photons are at telecom wavelengths, it is well adapted to applications in quantum communication.

quant-ph↗
arXiv2013

Narrowband Photon Pair Source for Quantum Networks

We demonstrate a compact photon pair source based on a periodically poled lithium niobate nonlinear crystal in a cavity. The cavity parameters are chosen such that the emitted photon pair modes can be matched in the region of telecom ultra dense wavelength division multiplexing (U-DWDM) channel spacings. This approach provides efficient, low-loss, mode selection that is compatible with standard telecommunication networks. Photons with a coherence time of 8.6 ns (116 MHz) are produced and their purity is demonstrated. A source brightness of 134 pairs(s.mW.MHz)$^{-1}$ is reported. The high level of purity and compatibility with standard telecom networks is of great importance for complex quantum communication networks.

quant-ph↗
arXiv2013

Simple, pulsed, polarisation entangled photon pair source

We report the realisation of a fibred polarisation entangled photon-pair source at 1560 nm based on a type-II non linear interaction and working in the picosecond regime. By taking advantage of a set of filters, we deterministically separate the photons and project them into wavelength separable states. A standard entanglement measurement with a net interference visibility close to 1, proves the relevance of our approach as an enabling technology for entanglement-based quantum communication.

quant-ph↗
arXiv2013

Polarization dependent, surface plasmon induced photoconductance in gold nanorod arrays

We report on the photoconductance in two-dimensional arrays of gold nanorods which is strongly enhanced at the frequency of the longitudinal surface plasmon of the nanorods. The arrays are formed by a combination of droplet deposition and stamping of gold nanorod solutions on SiO2 substrates. We find that the plasmon induced photoconductance is sensitive to the linear polarization of the exciting photons. We interpret the occurrence of the photoconductance as a bolometric enhancement of the arrays' conductance upon excitation of the longitudinal surface plasmon resonance of the nanorods.

cond-mat.mes-hall↗
arXiv2013

Generation of tunable wavelength coherent states and heralded single photons for quantum optics applications

Quantum optics experiments frequently involve interfering single photons and coherent states. In the case of multi-photon experiments this requires that all photons are frequency degenerate. We report a simple and practical approach to generate coherent states that can be readily tuned to any wavelength required, for example by non-degenerate photon pair creation. We demonstrate this by performing a two-photon (Hong-Ou-Mandel) interference experiment between a coherent state and a pure heralded single photon source. No spectral filtering is required on either source, the coherent state constrained by the pump and seed lasers and the heralded photon exploits non-local filtering. We expect that such an approach can find a wide range of applications in photonic based quantum information science.

quant-ph↗
arXiv2013

High efficiency coupling of photon pairs in practice

Multi-photon and quantum communication experiments such as loophole-free Bell tests and device independent quantum key distribution require entangled photon sources which display high coupling efficiency. In this paper we put forward a simple quantum theoretical model which allows the experimenter to design a source with high pair coupling efficiency. In particular we apply this approach to a situation where high coupling has not been previously obtained: we demonstrate a symmetric coupling efficiency of more than 80% in a highly frequency non-degenerate configuration. Furthermore, we demonstrate this technique in a broad range of configurations, i.e. in continuous wave and pulsed pump regimes, and for different nonlinear crystals.

quant-ph↗
arXiv2013

Two-photon interference between disparate sources for quantum networking

Quantum networks involve entanglement sharing between multiple users. Ideally, any two users would be able to connect regardless of the type of photon source they employ, provided they fulfill the requirements for two-photon interference. From a theoretical perspective, photons coming from different origins can interfere with a perfect visibility, provided they are made indistinguishable in all degrees of freedom. Previous experimental demonstrations of such a scenario have been limited to photon wavelengths below 900 nm, unsuitable for long distance communication, and suffered from low interference visibility. We report two-photon interference using two disparate heralded single photon sources, which involve different nonlinear effects, operating in the telecom wavelength range. The measured visibility of the two-photon interference is 80+/-4%, which paves the way to hybrid universal quantum networks.

quant-ph↗
arXiv2013

A complete characterisation of the heralded noiseless amplification of photons

Heralded noiseless amplifcation of photons has recently been shown to provide a means to overcome losses in complex quantum communication tasks. In particular, to overcome transmission losses that could allow for the violation of a Bell inequality free from the detection loophole, for Device Independent Quantum Key Distribution (DI-QKD). Several implementations of a heralded photon amplifier have been proposed and the first proof of principle experiments realised. Here we present the first full characterisation of such a device to test its functional limits and potential for DI-QKD. This device is tested at telecom wavelengths and is shown to be capable of overcoming losses corresponding to a transmission through $20\, \rm km$ of single mode telecom fibre. We demonstrate heralded photon amplifier with a gain $>100$ and a heralding probability $>83 % $, required by DI-QKD protocols that use the Clauser-Horne-Shimony-Holt (CHSH) inequality. The heralded photon amplifier clearly represents a key technology for the realisation of DI-QKD in the real world and over typical network distances.

quant-ph↗
arXiv2013

Experimental access to higher-order Zeeman effects by precision spectroscopy of highly charged ions in a Penning trap

We present an experimental concept and setup for laser-microwave double-resonance spectroscopy of highly charged ions in a Penning trap. Such spectroscopy allows a highly precise measurement of the Zeeman splittings of fine- and hyperfine-structure levels due the magnetic field of the trap. We have performed detailed calculations of the Zeeman effect in the framework of quantum electrodynamics of bound states as present in such highly charged ions. We find that apart from the linear Zeeman effect, second- and third-order Zeeman effects also contribute to the splittings on a level of 10^-4 and 10^-8, respectively, and hence are accessible to a determination within the achievable spectroscopic resolution of the ARTEMIS experiment currently in preparation.

physics.atom-ph↗