CONTRIBUTED TALKS

TUESDAY 9 NOVEMBER

Moderators: Rob Sewell & Daniel Sahagun-Sanchez

1. Carlos Diaz Mejía (UNAM)

Quantum Chaos in Many Body Systemas (Aubry Andre)

The theory behind quantum chaos and Eigenstate Thermalization Hypothesis(ETH) is deeply rooted in Random Matrix Theory,  nevertheless in quantum many body systems it is not clear if the dynamics could also exhibit quantum chaos. We demonstrate that the dynamics of the survival probability is a good aproach to characterize all  the possible initial states that show quantum chaos and the relation of these initial states to ETH

2. Sahory Andrea Canseco Jiménez (UNAM)

Quantum Speed Limit and Fermion Entanglement

The aim of the present contribution is to investigate, in detail, for bipartite systems of low dimensionality, the connection between entanglement and the speed of quantum evolution. We are going to focus our attention on  fermionic composite (bipartite) systems of lowest dimensionality. That is because in certain cases, entanglement helps to “speed up” the time evolution of composite systems.

3. Korbinian Kottmann (ICFO)

Variational Quantum Anomaly Detection: Finding phase transitions on a quantum computer

I will present our work on a variational quantum algorithm to map out the phase diagram of a quantum many body system that is simulated on a quantum computer in a direct way on-chip. I.e., the algorithm is performed on the same quantum computer the many-body system is simulated on in a native way. We demonstratesuccessful implementation in realistic noisy simulations and on a physical noisy 5-qubit quantum computer.

4. Eduardo Beattie (ICFO)

Towards detection of single erbium ions in a tunable fiber micro-cavity

Rare-earth ion-doped crystals constitute a promising platform for quantum information processing and networking. They feature exceptional spin coherence times to store information, narrow optical transitions to act as an interface to optical photons, and possibilities to realize quantum gates between single ion qubits. Coupling quantum emitters to optical cavities enables channeling the emission from the emitters into the cavity mode while decreasing their emission lifetime. This allows the realization of an efficient and high-rate spin-photon interface, while also increasing the indistinguishability of the emitted photons in the presence of dephasing.  In this work, by utilizing erbium-doped nanoparticles that emit at telecom wavelengths coupled to a fully tunable high-finesse fiber-based microcavity in a cryostat, we demonstrate an average Purcell factor greater than 100 for a very small ensemble of erbium ions (Purcell enhanced lifetime of 90 μs). Frequency selective excitation followed by fluorescence detection results in discrete features which indicate the sensitivity of the setup to few ions. Next steps involve isolating one such feature in a sparsely populated spectral region of the inhomogeneous line and measuring the auto-correlation function of the emitted photons. The presence of one or few ions can then be induced from the value of this function.   We have demonstrated with the previous version of our setup that we can control the Purcell factor and hence the emission rate of the ions on a timescale of hundreds of microseconds. Our current setup should enable us to reduce this time to a few tens of microseconds. If implemented at the single ion level, this ability will enable the generation of fully tunable narrowband single photons at telecom wavelengths, and quantum processing using single rare-earth-ions.

5. Diego Alberto Olvera Millán (UNAM)

Detection of Entanglement Using Neural Networks

Entanglement is an important resource for quantum technologies, but its detection and classification cannot be performed efficiently across different kinds of quantum states. In particular, quantum mixed states require computationally demanding methods, such as those of convex roof constructions. In this work, I train an artificial neural network(ANN) to perform the classification between entangled and separable two qubit states, using expected values of products of Pauli matrices as the entries of the feature vector, \vec{x}. The training is performed using only random pure states sampled from the invariant Haar measure. It is found that, using the 15 linearly independent products of Pauli matrices, an accuracy of 98% is achieved for states drawn from the same distribution, and the accuracy for states drawn from the Bures distribution can reach up to 80% (after applying regularization to the model). Using 4 non orthogonal products of the Pauli matrices, an accuracy of 91% is achieved for states sampled from the Haar distribution, and, when dealing with states sampled from the Bures distribution with purity and concurrence higher than 0.7, an accuracy of up to 84% is achieved.

6. Aikaterini Gratsea (ICFO)

Exploring the benefits of Quantum Perceptrons and Quantum Neural Networks

The rapid development of machine learning and quantum information gave rise to quantum machine learning which entails machine learning tasks performed (at least partially) on quantum computers. Recently, various works discussed several architectures for quantum perceptrons and quantum neural networks, but the abilities of such quantum machines remain debated. We explore the benefits of such quantum machines in three projects. In the first project, we focus on the storage capacity of quantum perceptrons implemented on noisy intermediate scale quantum (NISQ) devices. We apply techniques from statistical physics, and specifically Gardner program, to a quantum information problem. In the second project, we explore the expressive power of the aforementioned quantum perceptrons along with quantum neural networks on NISQ devices. We introduce the teacher-student scheme to systematically compare different architectures and find the type of functions that quantum models could learn. In the last project, we deviate from NISQ era and calculate the learning capability of different quantum neural networks. We define them as complete positive trace preserving maps with a fixed condition and apply Gardner program. We believe that the aforementioned projects will advance the fast-growing field of quantum machine learning.

7. Ana María Torres (UNIANDES)

Witnessing entangled two photon absorption in experiments based on the measurement of transmitted photon pairs

The process of Entangled Two-Photon Absorption (ETPA) has become an interesting topic due to possible applications in physics and biology [1,2]. Many questions have aroused regarding experiments in which the ETPA signal is obtained from measurements using a coincidence detection scheme to record the photon pairs transmitted by a sample. The results of two experiments developed at Los Andes University allow us to claim that the absorption signal observed with the coincidence counts scheme is due to ETPA.  In our experiments entangled photon pairs are obtained by means of the process of Spontaneous Parametric Down-Conversion (SPDC) using a BBO crystal. Photons pairs are sent to a sample of Rhodamine B (RhB) in methanol.  The experiments aim to measure the two-photon absorption signal under different filtering conditions. In the first experiment the intensity of the pump light is filtered using neutral density filters. From this data a clear two photon absorption signal, showing a linear dependence with the photon flux, is observed.  In the second experiment, neutral density filters are placed after the nonlinear crystal in order to filter the entangled photon pairs. In this case, the behavior observed is characteristic of uncorrelated photon pairs and no absorption signal is present under this filtering condition.  The fact that there is not absorption signal when filtering the SPDC photons but the two-photon absorption signal is present when filtering the pump light is an indication that we observed an ETPA process.

8. Benkos Komambakosy  Ramirez Balanta (U. QUINDIO)

Gravedad Modificada (MOG)

MOG estudia la posibilidad y consecuencias de modificar la fuerza de gravedad. A través de esta hipótesis se han podido explicar las curvas de rotación de las galaxias, convirtiéndose en una candidata rival a la de materia oscura.

9. Carlos Efrain Quintero Narvaez (UNAM)

Qudit Gates and Noncommutative Tori

Introduction to the the theory of quantum computing with qudits which are quantum units that have more than two level as opposed to standard qubits. Here we present some useful notations and algorithms analog to those of standard quantum computing with qubits using instead these many-level quantum units we just mentioned (qudits). After that we present the formalism of abstract space-time algebras and how they are used in standard quantum computing. Finally we show how an analog of space-time algebras can be realized using algebraic objects known as noncommutative tori as seen in Yu. Vlasov’s work.

10. Víctor Hernán Torres Brauer (UNAM)

Guaranteed emergency of genuine entanglement in three qubit evolving system

Multipartite entanglement has been shown to be of particular relevance for a better understanding and exploitation of the dynamics and flow of entanglement in multiparty systems. This calls for analysis aimed at identifying the appropriate processes that guarantee the emergence of multipartite entanglement in a wide range of scenarios. Here we carry on such analysis considering a system of two initially entangled qubits, one of which is let to interact with a third qubit according to an arbitrary unitary evolution. We establish necessary and sufficient conditions on the corresponding Kraus operators, to discern whether the evolved state pertains to either one of the classes of 3-qubit pure states that exhibit some kind of entanglement, namely biseparable, W-, and GHZ- genuine entangled classes. Our results provide a classification of the Kraus operators according to their capacity of producing multipartite correlations and pave the way for determining the particular interactions that must be implemented in order to create, enhance and distribute entanglement in a specific manner.

11. Homar Rivera (UNAM)

Electrostatic interactions involving exotic long-range Rydberg molecules

A long-range Rydberg molecule (LRRM) is formed by a Rydberg atom and a ground state atom.  Using the multipole expansion of the electrostatic interaction in prolate spheroidal coordinates, approximate and compact expressions of the electrostatic potential that determine the chemistry of trilobite and butterfly LRRM are explored. It is shown that even the prolate spheroidal monopole term can be used to describe general features of the potential generated by an LRRM at short distances. It is also shown that even at long separations that allow a perturbative description of the intermolecular interaction between two LRRM, the convergence of the multipole prolate spheroidal expansion is faster than that of its spherical analogue.

WEDNESDAY 10 NOVEMBER

Moderators: Alejandra Valencia & Juan Pérez Torres

1. Chenglong You (Louisiana State University)

Scalable multiphoton quantum metrology with neither pre- nor post-selected measurements

We demonstrate the scalable multiphoton quantum metrology protocol for quantum-enhanced phase estimation without pre- and post-selected measurements. Our experiment, with an overall efficiency of 82%, utilizes two-mode squeezed vacuum states and photon-number-resolving detection to surpass the standard quantum limit.

2. Mingyuan Hong (Louisiana State University)

Observation of the modification of quantum statistics of plasmonic systems

For almost two decades, researchers have observed the preservation of the quantum statistical properties of bosons in a large variety of plasmonic systems. In addition, the possibility of preserving nonclassical correlations in light-matter interactions mediated by scattering among photons and plasmons stimulated the idea of the conservation of quantum statistics in plasmonic systems. It has also been assumed that similar dynamics underlie the conservation of the quantum fluctuations that define the nature of light sources. So far, plasmonic experiments have been performed in nanoscale systems in which complex multiparticle interactions are restrained. Here, we demonstrate that the quantum statistics of multiparticle systems are not always preserved in plasmonic platforms and report the observation of their modification. Moreover, we show that optical near fields provide additional scattering paths that can induce complex multiparticle interactions. Remarkably, the resulting multiparticle dynamics can, in turn, lead to the modification of the excitation mode of plasmonic systems. These observations are validated through the quantum theory of optical coherence for single- and multi-mode plasmonic systems. Our findings unveil the possibility of using multiparticle scattering to perform exquisite control of quantum plasmonic systems.

3. Maria Fernanda Morris Garcés (UNIANDES)

Implementation of an intense source of frequency correlated photon pairs using a PPKTP crystal

The implementation of an intense source of correlated photon pairs using a PPKTP crystal requires two main parts: the SPDC downward parametric spontaneous emission process taking into account the quasi-phase matching conditions and a single-mode pump source with profile Gaussian stabilized at a single frequency. In this project a theoretical study of the SPDC process and the necessary conditions for an intense production of pairs of correlated photons is made; in particular, its dependence on the temperature of the crystal and the pumping wavelength. A single frequency pump laser source with a Gaussian profile focused on the PPKTP crystal is implemented. The source of photon pairs is characterized spatially, in intensity and in frequency. An intense source of photon pairs is obtained with a hit rate per mW of pumping power of $ 199 \ pm $ 1 kHz / mW which is at least three times greater than the pair production rate in the SPDC process. using a traditional non-linear crystal like BBO.

4. Daniel Sabogal (UNIANDES)

Taking advantage of noise in quantum key distribution

At present time, improving security in the transmission of information is an important fact.  Conventional cryptographic systems cannot ensure confidentiality if there is enough computational power to wipe out security. One alternative is  to use the laws of quantum mechanics. For example, the BB84 protocol, in which single-photons are sent in an ideal quantum channel in such a way that two parties can get privacy. Nevertheless, the experimental implementation of the BB84 protocol deals with problems like noise, imperfect devices and the lack of a single-photon source on demand.  Efforts have been made to relax these constrains, like the use of alternative sources and the search for a deep understanding of noise. In this talk, it is presented  a method to improve the security of the BB84 by taking advantage of the noise induced by the environment. Furthermore, he implementation of a decoy-state source, as an alternative to single-photon sources,  in the BB84 protocol will be discussed.

5. Juan Carlos Obeso Jureidini (UNAM)

Spatial structure of a two-component Fermi gas throughout the BEC-BCS crossover

We analyze the spatial structure of a homogeneous mixture of a two-component Fermi gas, where the modulation of an effective interaction allows a crossover from a Bardeen-Cooper-Schrieffer (BCS) superfluid to a Bose-Einstein condensate (BEC) of composite bosons. The information about the spatial structure is extracted from three functions: The BCS pair wave function, the density correlation function of particles with equal components and the density correlation function of particles with different components. In particular, we present their large-distance behavior, which corresponds to a well-defined oscillatory behavior with an exponential decay. The consideration of these three functions gives a complete picture of the pairing phenomenon throughout the crossover [J.C. Obeso-Jureidini and V. Romero-Rochín, Phys. Rev. A 101, 033619 (2020)].

6. Philipp Stammer (ICFO)

High photon number entangled state with high harmonic generation

We present a theoretical study on the generation of entangled coherent states and of coherent state superpositions, with photon numbers and energies, orders of magnitude higher than those provided by the current technology. This is achieved by utilizing a quantum mechanical multimode description of the single- and two-color intense laser field driven process of high harmonic generation in atoms. It is found that all field modes involved in the high harmonic generation process are entangled, and upon performing a quantum operation, leads to the generation of high photon number non-classical coherent state superpositions spanning from the extremeultraviolet to the far infrared spectral region. These states can be considered as a new resource for fundamental tests of quantum theory and quantum information processing.

7. Harold Alberto Rojas Páez (UNIANDES)

Cat-States-Like Wigner Functions by means of Classical Fields

The Wigner distribution is useful to describe both quantum and classical signals. In the quantum domain, it gives a trace of the quantum character of the system and in the classical domain allows retrieving simultaneously information about conjugated variables as time and frequency. Other tools to describe signals are the Fourier Transform (FT) and its generalization the Fractional Order Fourier Transform (FrFT). A tomographic reconstruction of the Wigner distribution can be performed by using an appropriate collection of different order Fractional Fourier Transforms (FrFT). In this talk, we present such a reconstruction for the Wigner distribution in position and transverse momentum variables. We will present a theoretical description of the reconstruction method and the preliminary experimental results for a field whose Wigner distribution resembles the one associated to what is called a Cat state. The topic discussed throughout this talk goes along the lines of finding classical analogies of quantum phenomena with implications in the optical simulation of quantum systems.

8. Jeimmy Alejandra Alarcón Carvajal (UNIANDES)

Multiphoton interference of distinguishable photons based on photonic inner mode structure

Many quantum-based applications rely on quantum interference between photons. The interference phenomena can be studied in different degrees of freedom, for example in time, polarization, and spatial variables such as orbital angular momentum and transverse momentum. On the other hand, interference phenomena can be observed between indistinguishable photons in a given degree of freedom. Moreover when photons are distinguishable in a variable, interference can be also observed in its conjugated variable. The aim of this project is to analyze interference in transverse momentum variables via spatially resolved correlation measurements. Particular interest will be devoted to study two-photon interference in a linear optical system of input photons differing in a given inner degree of freedom, explicitly two distinguishable photons in position. This work will further contribute to the understanding of interference in a phenomenological way, which is crucial for the implementation of an experimental scheme. A bigger contribution of this work will be an advance in the understanding and implementations of quantum interference in quantum technologies.

9. Gustavo Armendáriz Peña (UNAM)

Poissonian and chaotic statistics production from single photons

Nowadays, quantum technologies require determined quantum states and on a specific statistic to work efficiently. One of those statistics has practically not been studied: the one characterized by 1/f noise using quantum states of light. Due to our work line and interests in quantum information technologies, we decided to produce this type of statistics using single photons. To do this, we first numerically simulate the effect of sending individual photons through a network of beam splitters (BS) by controlling the reflection (R) and transmission (T) coefficients. Once we determine the values of R and T, we also test how robust the system is for random stochastic variations (in a 3 and a 5 BS network). The next step is the manufactured of BS on photonic chips (waveguides) to test the numerical results. To this day, we have already calculated and measured the basic experimental parameters of PDMS microfabricated waveguides: attenuation coefficient, numerical aperture, acceptance angle and geometric arrangement of the guides for BS by evanescent field. Moreover, the achievement of this design has to do with a very common problem: coupling optical fibers light into waveguides. We solved it introducing the optical fiber in the same canal where the waveguide was manufactured. Then, we got direct coupling. We expect to get experimental results from the first BS on chip within the next two months.

10. José Ernesto Alba Arroyo (UNAM)

Weber number and the outcome of binary collisions between quantum droplets

We analyze the binary collision of both homonuclear and heteronuclear quantum droplets under feasible conditions. Using Thouless variational theorem we estimate the expected excitation energy of surface excitations for the ground state of a spherical droplet, resulting on a model for the surface tension. This in turn lets us calculate the Weber number of droplets involved in several collisions. We find that the Weber number characterizes well the outcome of head-on collisions even when three-body losses are taken into account.

11. Natalia Herrera Valencia (HERRIOT WATT)

Unscrambling entanglement through a complex medium

The curious phenomenon of entanglement has proven to be an essential resource for applications in quantum computation, quantum communications, and quantum sensing.  When states of light are involved, their high-dimensional structure offers high information capacity and noise robustness, enhancing the implementation of quantum technologies.  In this talk, I will discuss novel methods to engineer and efficiently characterise the entanglement of high-dimensional states of light. Furthermore, I’ll present the transport of this type of entanglement through a complex scattering medium, showcasing the potential of this platform in the control and manipulation of large quantum systems.