Irreversibility in quantum maps with decoherence

The Bolztmann echo (BE) is a measure of irreversibility and sensitivity to perturbations for non-isolated systems. Recently, different regimes of this quantity were described for chaotic systems. There is a perturbative regime where the BE decays with a rate given by the sum of a term depending on the accuracy with which the system is time-reversed and a term depending on the coupling between the system and the environment. In addition, a parameter independent regime, characterised by the classical Lyapunov exponent, is expected. In this paper we study the behaviour of the BE in hyperbolic maps that are in contact with different environments. We analyse the emergence of the different regimes and show that the behaviour of the decay rate of the BE is strongly dependent on the type of environment.Comment: 13 pages, 3 figures

A highly stable and fully tunable open microcavity platform at cryogenic temperatures

Open-access microcavities are a powerful tool to enhance light–matter interactions for solid-state quantum and nanosystems and are key to advance applications in quantum technologies. For this purpose, the cavities should simultaneously meet two conflicting requirements—full tunability to cope with spatial and spectral inhomogeneities of a material and highest stability under operation in a cryogenic environment to maintain resonance conditions. To tackle this challenge, we have developed a fully tunable, open-access, fiber-based Fabry–Pérot microcavity platform that can be operated under increased noise levels in a closed-cycle cryostat. It comprises custom-designed monolithic micro- and nanopositioning elements with up to mm-scale travel range that achieve a passive cavity length stability at low temperature of only 15 pm rms in a closed-cycle cryostat and 5 pm in a more quiet flow cryostat. This can be further improved by active stabilization, and even higher stability is obtained under direct mechanical contact between the cavity mirrors, yielding 0.8 pm rms during the quiet phase of the closed-cycle cryocooler. The platform provides the operation of cryogenic cavities with high finesse and small mode volume for strong enhancement of light–matter interactions, opening up novel possibilities for experiments with a great variety of quantum and nanomaterials

Dynamic control of Purcell enhanced emission of erbium ions in nanoparticles

The interaction of single quantum emitters with an optical cavity enables the realization of efficient spin-photon interfaces, an essential resource for quantum networks. The dynamical control of the spontaneous emission rate of quantum emitters in cavities has important implications in quantum technologies, e.g., for shaping the emitted photons’ waveform or for driving coherently the optical transition while preventing photon emission. Here we demonstrate the dynamical control of the Purcell enhanced emission of a small ensemble of erbium ions doped into a nanoparticle. By embedding the nanoparticles into a fully tunable high finesse fiber based optical microcavity, we demonstrate a median Purcell factor of 15 for the ensemble of ions. We also show that we can dynamically control the Purcell enhanced emission by tuning the cavity on and out of resonance, by controlling its length with sub-nanometer precision on a time scale more than two orders of magnitude faster than the natural lifetime of the erbium ions. This capability opens prospects for the realization of efficient nanoscale quantum interfaces between solid-state spins and single telecom photons with controllable waveform, for non-destructive detection of photonic qubits, and for the realization of quantum gates between rare-earth ion qubits coupled to an optical cavity

Detection of single ions in a nanoparticle coupled to a fiber cavity

Many quantum information protocols require the storage and manipulation of information over long times, and its exchange between nodes of a quantum network across long distances. Implementing these protocols requires an advanced quantum hardware, featuring, for example, a register of long-lived and interacting qubits with an efficient optical interface in the telecommunication band. Here we present the Purcell-enhanced detection of single solid-state ions in erbium-doped nanoparticles placed in a fiber cavity, emitting photons at 1536 nm. The open-access design of the cavity allows for complete tunability both in space and frequency, selecting individual particles and ions. The ions are confined in a volume two orders of magnitude smaller than in previous realizations, increasing the probability of finding ions separated only by a few nanometers which could then interact. We report the detection of individual spectral features presenting saturation of the emission count rate and linewidth, as expected for two-level systems. We also report an uncorrected $g^{(2)} \left ( 0 \right )$ of 0.24(5) for the emitted field, confirming the presence of a single emitter. Our fully fiber-integrated system is an important step towards the realization of the initially envisioned quantum hardware

Human papillomavirus (HPV) DNA in penile carcinomas in Argentina: Analysis of primary tumors and lymph nodes

Among sexually transmitted diseases, infection by human papillomavirus (HPV) has become one of the most important. On the other hand, though epidemiological data show that some HPV types are closely associated with cervical cancer, few reports have been found with reference to penile carcinoma because of its rare occurrence. The aim of this study was to investigate the relationship between HPV infection and penile cancer in Argentina. A retrospective study was carried out on 38 white men with penile squamous-cell carcinoma. Sixty-five archival fixed biopsies taken from 34 primary penile tumors, 25 nodal metastases, 1 skin “satellite” metastasis and 5 histologically normal lymph nodes were used as specimens. HPV detection and typing were carried out by the polymerase chain reaction (PCR) using generic primers, combined with single-stranded conformational polymorphism (SSCP) analysis. HPV DNA was found in 71% patients, corresponding 81% of them to “high risk” types, with predominance of HPV 18. Both primary tumors and metastases showed concordance of HPV occurrence and type in both lesions. In 3 patients, HPV 16 was detected not only in primary tumors and metastases, but also in histologically normal lymph nodes. Our data indicate that most penile carcinomas in Argentine patients are etiologically related to HPV, especially to “high risk” genital types. The agreement in HPV detection between primary tumors and metastases suggests a potential viral role in tumor progression. HPV detection in otherwise histologically normal lymph nodes might be useful as early marker of a metastatic process.Fil: Picconi, María A.. Dirección Nacional de Instituto de Investigación. Administración Nacional de Laboratorio e Instituto de Salud “Dr. C.G. Malbrán”; ArgentinaFil: Eijan, Ana Maria. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Universidad de Buenos Aires; ArgentinaFil: Distéfano, Angélica L.. Dirección Nacional de Instituto de Investigación. Administración Nacional de Laboratorio e Instituto de Salud “Dr. C.G. Malbrán”; ArgentinaFil: Pueyo, Silvia. Provincia de Buenos Aires. Ministerio de Salud. Hospital Materno Infantil de San Isidro. Servicio de Dermatología; ArgentinaFil: Alonio, Lidia Virginia. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Dirección Nacional de Instituto de Investigación. Administración Nacional de Laboratorio e Instituto de Salud “Dr. C.G. Malbrán”; ArgentinaFil: Gorostidi, Susana. Universidad de Buenos Aires; ArgentinaFil: Teyssié, Angélica R.. Dirección Nacional de Instituto de Investigación. Administración Nacional de Laboratorio e Instituto de Salud “Dr. C.G. Malbrán”; ArgentinaFil: Casabone, Bernardo Adalberto. Universidad de Buenos Aires; Argentin

Optical coherence properties of Kramers' rare-earth ions at the nanoscale for quantum applications

Rare-earth (RE) ion doped nano-materials are promising candidates for a range of quantum technology applications. Among RE ions, the so-called Kramers' ions possess spin transitions in the GHz range at low magnetic fields, which allows for high-bandwidth multimode quantum storage, fast qubit operations as well as interfacing with superconducting circuits. They also present relevant optical transitions in the infrared. In particular, Er$^{3+}$ has an optical transition in the telecom band, while Nd$^{3+}$ presents a high-emission-rate transition close to 890 nm. In this paper, we measure spectroscopic properties that are of relevance to using these materials in quantum technology applications. We find the inhomogeneous linewidth to be 10.7 GHz for Er$^{3+}$ and 8.2 GHz for Nd$^{3+}$, and the excited state lifetime T$_1$ to be 13.68 ms for Er$^{3+}$ and 540 $\mu$s for Nd$^{3+}$. We study the dependence of homogeneous linewidth on temperature for both samples, with the narrowest linewidth being 379 kHz (T$_2$ = 839 ns) for Er$^{3+}$ measured at 3 K, and 62 kHz (T$_2$ = 5.14 $\mu$s) for Nd$^{3+}$ measured at 1.6 K. Further, we investigate time-dependent homogeneous linewidth broadening due to spectral diffusion and the dependence of homogeneous linewidth on magnetic field, in order to get additional clarity of mechanisms that can influence the coherence time. In light of our results, we discuss two applications: single qubit-state readout and a Fourier-limited single photon source.Comment: 9 pages, 5 figure

Cavity-enhanced spectroscopy of a few-ion ensemble in Eu3+:Y2O3

We report on the coupling of the emission from a single europium-doped nanocrystal to a fiber-based microcavity under cryogenic conditions. As a first step, we study the properties of nanocrystals that are relevant for cavity experiments and show that embedding them in a dielectric thin film can significantly reduce scattering loss and increase the light-matter coupling strength for dopant ions. The latter is supported by the observation of a fluorescence lifetime reduction, which is explained by an increased local field strength. We then couple an isolated nanocrystal to an optical microcavity, determine its size and ion number, and perform cavity-enhanced spectroscopy by resonantly coupling a cavity mode to a selected transition. We measure the inhomogeneous linewidth of the coherent D-5(0)-F-7(0) transition and find a value that agrees with the linewidth in bulk crystals, evidencing a high crystal quality. We detect the fluorescence from an ensemble of few ions in the regime of power broadening and observe an increased fluorescence rate consistent with Purcell enhancement. The results represent an important step towards the efficient readout of single rare earth ions with excellent optical and spin coherence properties, which is promising for applications in quantum communication and distributed quantum computation

Two ions coupled to an optical cavity : from an enhanced quantum computer interface towards distributed quantum computing

Verteiltes Quantenrechnen stellt eine Möglichkeit zur Verbesserung der Rechenleistung von Quantencomputern dar, erfordert jedoch Verschränkung zwischen den einzelnen Bestandteilen des Quantennetzwerks. In unserer Forschungsgruppe wurden zwei Alternativen der Verknüpfung ionenbasierter Quantencomputer mit Hilfe von optischen Resonatoren demonstriert: Verschränkung von einem Ion mit einem Photon und die Abbildung des Quantenzustands eines Ions auf den eines einzelnen Photons. In dieser Arbeit erweitern wir einerseits die erste Methode und verschränken zwei Ionen, die sich innerhalb desselben optischen Resonators befinden. Die Verschränkung wird effizient erzeugt und ist angekündigt. Außerdem müssen die beiden Ionen sich nicht im selben Resonator befinden, sodass unser Ergebnis einen Baustein für die effiziente Erzeugung von Verschränkung entfernter ionenbasierter Quantencomputer darstellt. Im zweiten Teil der Arbeit wird diskutiert, wie kollektive Effekte verwendet werden können, um die Leistung einer resonatorbasierten Quantenschnittstelle zu verbessern. Wir zeigen, dass bei der Verwendung eines sogenannten superradianten Zustands die Kopplungsstärke zwischen den beiden Ionen und dem Resonator im Vergleich mit einem einzelnen Ion effektiv gesteigert wird. Komplementär dazu wird gezeigt, dass ein Zustand der zwei Ionen erzeugt werden kann, der eine stark reduzierte Kopplungsstärke an den Resonator aufweist, das ist, ein subradianter Zustand. Abschließend wird die gesteigerte Kopplungsstärke des superradianten Zustands verwendet, um eine verbesserte Version des Protokolls zur Zustandsabbildung zu demonstrieren. Aus dem verwendeten experimentellen Aufbau und einem zweiten Aufbau, der sich in der Konstruktionsphase befindet, wird in naher Zukunft ein Quantennetzwerk aufgebaut werden. Das in der vorliegenden Arbeit beschriebene Protokoll zur Verschränkung zweier Ionen wird verwendet werden, um Ionen in den zwei räumlich getrennten Aufbauten zu verschränken. In diesem Experiment müssen die Photonen, die von den Ionen erzeugt werden ununterscheidbar sein. Diese Voraussetzung kann erfüllt werden, indem die Form der photonischen Wellenpakete mit Hilfe kollektiver Effekte kontrolliert wird.Distributed quantum computing, an approach to scale up the computational power of quantum computers, requires entanglement between nodes of a quantum network. In our research group, two building blocks of schemes to entangle two ion-based quantum computers using cavity-based quantum interfaces have recently been demonstrated: ion-photon entanglement and ion-photon state mapping. In this thesis work, we extend the first building block in order to entangle two ions located in the same optical cavity. The entanglement generated by this protocol is efficient and heralded, and as it does not rely on the fact that ions interact with the same cavity, our results are a stepping stone towards the efficient generation of entanglement of remote ion-based quantum computers. In the second part of this thesis, we discuss how collective effects can be used to improve the performance of a cavity-based quantum interface. We show that by using two ions in the so-called superradiant state, the coupling strength between the two ions and the optical cavity is effectively increased compared to the single-ion case. As a complementary result, the creation of a state of two ions that exhibits a reduced coupling strength to the optical cavity, i.e., a subradiant state, is shown. Finally, we demonstrate a direct application of the increased coupling strength that the superradiant state exhibits by showing an enhanced version of the ion-photon state mapping process. By using the current setup and a second one that is being assembled, we intend to build a quantum network. The heralded ion-ion entanglement protocol presented in this thesis work will be used to entangle ions located in both setups, an experiment that requires photons generated in both apparatuses to be indistinguishable. Collective effects then can be used to modify the waveform of photons exiting the cavity in order to effect the desired photon indistinguishability.vorgelegt von Bernardo CasaboneZsfassung in engl. SpracheInnsbruck, Univ., Diss., 2015OeBB(VLID)42186

Efficient cavity-assisted storage of photonic qubits in a solid-state quantum memory

We report on the high-efficiency storage and retrieval of weak coherent optical pulses and photonic qubits in a cavity-enhanced solid-state quantum memory. By using an atomic frequency comb (AFC) memory in a $Pr^{3+}:Y_2 SO_5$ crystal embedded in a low-finesse impedance-matched cavity, we stored weak coherent pulses at the single photon level with up to 62% efficiency for a pre-determined storage time of 2 $\mu$s. We also confirmed that the impedance-matched cavity enhances the efficiency for longer storage times up to 70 $\mu$s. Taking advantage of the temporal multimodality of the AFC scheme, we then store weak coherent time-bin qubits with (51+-2)% efficiency and a measurement-device limited fidelity over (94.8+-1.4)% for the retrieved qubits. These results represent the most efficient storage in a single photon level AFC memory and the most efficient qubit storage in a solid-state quantum memory up-to-date.Comment: 7 pages, 5 figure, 1 tabl