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The Quantum Technologies community in Spain

posted Jan 1, 2017, 4:29 AM by Juan Jose Garcia-Ripoll

What follows is a summary of the results from a poll on the community of quantum technologies in Spain, which covers all of the groups in the RICE network, as well as other groups who did not feel completely identified with our network denomination, but have a strong scientific overlap. The poll is limited in its scope and depth, but it offers sufficient information to do a thorough analysis of the community and its state. It is for this reason that I would like to thank all participants for their collaboration and hope that this document be useful for a productive discussion in 2017. Finally, note that the text below arises entirely from my personal analysis of the data and does not reflect any policy or view from neither the network, nor my employers.

Juan José García Ripoll
January 2017

Group composition and topics

Our network, RICE, was born with the words "Quantum Information" in it, but it has always been a collection of groups working in overlapping topics, such as quantum computing, quantum simulation, quantum sensing... In essence, what is nowadays known as "quantum information technologies": a more inclusive denomination that includes all technologies that benefit from quantum effects, such as entanglement, squeezing, etc.

Understanding this, the poll consulted all participants using the broader list of topics which are included both in the Quantum Manifesto as well as in the Quantum Roadmap. The outcome is as follows:

As evident from the chart, research in Spain covers a variety of topics --basically all from the roadmap. However, many of those topics are covered by more groups working in theoretical aspects (60%), than in experiments (40%).

It is also important to remark the large number of groups that work in the so called enabling technologies, which are setups (photonic crystals, lasers, quantum dots, etc) that are essential for developing QT, but which are not converted into QT setups in those groups. This is a potential that should not be underestimated, both for growth and consolidation of QT in Spain, but also because any of those technologies have very short-term applications in the productive and economic system.

Finally, QT has also overlap with a broad variety of communities, all of which are represented in RICE.

Figures: funding, staff, etc.

The following analysis focuses exclusively on national funding. We believe that a strong national support is essential for international competitiveness, specially now that Europe is adopting a new, global strategy that distinguishes between focused efforts, productive economy and basic science (the latter being mostly a responsability of the member states).

In Spain, national funding happens mostly through the Plan Estatal de Investigación, wich funds three-year projects that are broad, sometimes supporting whole departments. However, the poll was explicit in requesting real figures of all national funding that is actually devoted to topics in the Quantum Manifesto or Flagship topics, as well as providing details on the size of the groups, distinguishing between permanent and temporary positions.
The scatter plot of the 33 groups which contributed to the poll shows a wide dispersion of funding averages, but a more detailed analysis shows a somewhat worrying picture.

Postdocs & PhDs247145102
Funding per year€1,400,000€800,000€600,000
Average per staff (permanent)€16,000€18,000€13,000
Average per researcher (all)€4,000€4,000€4,000
Desired total funding€3,900,000€2,300,000€1,600,000
Desired avg. per staff€42,000€49,000€35,000

In this picture, all groups have a very low average funding per researcher. This implies that national fundeing cannot really sustain even a 12% of the personnel costs. This image is also consistent with the fact that many of the groups above depend on international funds for 50% to 80% of the costs, an unsustainable situation.

Equally worrying is the fact that experimental funding is worse than theoretical one. We have seen above the lack of experimental groups in key areas, such as quantum communication, simulation and computing. This is due to the fact that national funds cannot sustain stable, long term research in these fields with a funding as low as 13k€ per staff.

Indeed, it is not uncommon in these calls to see the budget of a complete experiment be cut but 40% or 60%, implying that the experimentalist has to find the remaining funds elsewhere. Such a situation is not consistent witha picture of "finalist" projects to achieve specific goals, but with a view of funding as "core funding", or minimal resources for subsistence.


We also have made a brief poll on activities that should be pursued by the network. Some of the ideas had already been discussed either in RICE's meetings or in the meetings sponsored by the Spanish Secretary of Science and Innovation (So called Foros Tecnológicos). The obvious winners in support are (i) a joint network or some other coordination instrument and (ii) promoting quantum technology to its own strategic research topic within the Retos program.

We expect that RICE, or its successor, will be able to fulfill partially this list and expect that those who declare some interest will help us in doing so.

Space-time and entanglement

posted Apr 18, 2016, 1:04 PM by Juan Jose Garcia-Ripoll

Javier Molina-Vilaplana.
Associate Professor. Universidad Politécnica de Cartagena.
Whenever two very different areas of theoretical physics are found to be described by the same mathematical structures, it frequently leads to discover unexpected insights on both sides. This brief overview tries to explain why physicists in the areas of quantum gravity and string theory, especially those interested in the quantum structure of space-time are taking advantage from the knowledge of the structure of the quantum entanglement encoded in the wave-functions of quantum many body systems and tools such as tensor networks, initially devised by physicists in the area of quantum information.

Quantum entanglement is the unique correlation allowed by quantum mechanics that Einstein famously called “spooky action at a distance.” Operationally speaking, entanglement means that information in an entangled quantum state is not stored in the individual parts at all, but only in the correlations among the parts. Entanglement is the major feature studied by quantum information science. It is the central concept underlying the ideas of quantum computers and quantum cryptography and lately it has also been successfully applied in classifying exotic phases of quantum matter. In addition, we have begun recently to understand how entanglement may be also the key to apprehend how space-time itself emerges from underlying microscopic quantum building blocks.

Indeed, any theory of quantum gravity faces strong conceptual problems due to the wild quantum fluctuations in the geometry of space-time that are supposed to free-run at the Planck scale. As one probes this shortest possible distance, space-time looks less and less like space-time. In words of physicist John Preskill, “it’s not really geometry anymore. It’s something else, an emergent thing that arises from something more fundamental.” What it has been recently proposed is that the fundamental threads from which a space-time fabric would emerge amount to the entanglement distribution between the degrees of freedom of an underlying and in some sense, more fundamental quantum theory.

In 2010 Mark Van Raamsdonk a string theorist at British Columbia, proposed a thought experiment to illustrate the critical role of entanglement in the formation of space-time. He found that disentangling the degrees of freedom of two contiguous regions of space-time is tantamount to disconnecting the regions altogether. In other words, space-time begins to tear itself apart, in much the same way that stretching a wad of gum by both ends yields a pinched-looking point in the center as the two halves move farther apart. Contrarily, by entangling distant degrees of freedom located at separate regions establishes spatial connections between them; as Van Raamsdonk says “if you wanted to build up a space-time, you’d want to start entangling qubits together in particular ways.”

Remarkably, these ideas have a natural arena to play with in the field of tensor network. A tensor network is a mathematical representation of the wave-function of a system made of a large number of interacting quantum constituents (qubits, electrons, spins…). As the data stored in the accounting department of a company can be understood as a reliable representation of the company’s state, a tensor network describes the state of the quantum many body system by, in some sense, providing a detailed account on how the quantum entanglement between the different constituents of the system is distributed.

There are many different types of tensor networks, but the kind of tensor networks much theorists are actually interested in is the MERA (multi-scale entanglement renormalization ansatz). Remarkably, it has been realized that the entanglement patterns within MERA can be represented as a diagram with the hyperbolic geometry intrinsic to the holographic proposals in string theory. This has led to the proposal that curved space-times may emerge quite naturally from entanglement in tensor networks via holography and that space-time, may be understood as a geometrical representation of this quantum information.

Within this background of ideas, questions related with, or relating the emergence of space-time symmetries (Poincarè, SUSY, conformal...) from lattice field theories, quantum and classical simulations for generic Renormalization Group flows and the emergence of geometry in the context of holography and tensor networks will be scrutinized by a miscellanea of researchers in the next years.

Un Lego cuántico y relativista

posted Dec 3, 2015, 3:06 AM by Juan Jose Garcia-Ripoll

por Carlos Sabín, IFF-CSIC

¿Qué falta por hacer en el campo de la física teórica? Hace ya un siglo que el ser humano fue capaz de alcanzar dos grandes cimas de pensamiento: por un lado, la teoría de la relatividad especial y general; por otro, la mecánica cuántica. Por separado, así como combinadas en la muy exitosa teoría cuántica de campos, estas dos teorías nos permiten predecir el comportamiento de la Naturaleza en una variedad de regímenes que resulta bastante exótica para nuestra experiencia cotidiana: desde lo infinitesimalmente pequeño e insoportablemente frío hasta la estructura de nuestro Universo a gran escala. De esta manera el paradigma de la física newtoniana se amplió para abarcar aquello que estaba mucho más allá de los estrechos confines de nuestra percepción. 

De manera natural, los físicos teóricos han intentado desde entonces integrar ambas teorías en un mismo paradigma que, incluyéndolas a las dos, las desborde y termine así de completar nuestra comprensión de los mecanismos fundamentales de la Naturaleza. Como ya hemos indicado, relatividad y teoría cuántica se combinan dentro de la teoría cuántica de campos, cuyo poder de predicción es tal que ha sido capaz de conducir al descubrimiento de nuevas partículas elementales, como el bosón de Higgs. Sin embargo, esto es sólo posible en la medida en que es posible ignorar un último ingrediente de la realidad: orgullosa y distante cual irreductible aldea gala, la fuerza de la gravedad resiste los embates expansionistas de la teoría cuántica, capaces hasta ahora de someter bajo un mismo marco teórico a las otras tres fuerzas fundamentales de la Naturaleza. No tenemos teoría del todo, no entendemos la gravedad a nivel cuántico y eso nos impide acceder a algunas esquinas de la realidad: pequeños agujeros negros, pequeños universos.

Ante esta perspectiva, los físicos teóricos tenemos varias opciones. Por ejemplo, podemos permanecer obedientemente entre las cómodas y familiares paredes de nuestra habitación, jugando con juguetes cuyo comportamiento conocemos en todo detalle. También podemos asomarnos a la ventana, a la frontera de lo que conocemos e intentar vislumbrar lo que hay fuera. Los juguetes para hacer esto último son cada vez más sofisticados y caros: redes de telescopios gigantes combinados para observar los violentos suburbios de un agujero negro, grandes anillos donde las partículas se aceleran hasta la velocidad de la luz y chocan, dejando un rastro en el que intentamos vislumbrar nuevas partículas, dimensiones y simetrías, monstruosos interferómetros en los que buscamos detectar el efecto minúsculo de una ondulación del espacio-tiempo en la trayectoria de un haz láser… Y otros muchos experimentos de gran escala en los que rastreamos eventos ignotos con nombres formidables: ¡materia oscura!, ¡axiones!, ¡supersimetría!, ¡desintegraciones beta dobles sin neutrinos!…

Hay también una tercera vía, al menos (muy adecuada para aquellos que no manejamos grandes presupuestos): tras echar un vistazo a la ventana, volver a tu habitación y usar los juguetes como un Lego, es decir, usarlos para construir el mundo que, mitad percibido y mitad imaginado, has vislumbrado ahí fuera. Para esto, entre otras muchas cosas, sirven las simulaciones cuánticas, un área emergente de la física en la que se usan sistemas cuánticos que somos capaces de manipular en el laboratorio para emular a otros sistemas cuánticos (o al menos algunas de sus propiedades) a los que no tenemos tan fácil acceso. Por supuesto, los simuladores cuánticos tienen importantes aplicaciones tecnológicas, y, de hecho, podemos entenderlos como un ejemplo de ordenador cuántico dedicado a resolver únicamente un problema concreto. Pero también pueden ser un Lego para explorar las fronteras de la física teórica.

Una de esas fronteras es la relación entre efectos cuánticos y relativistas en un mismo sistema físico: por ejemplo, el efecto de grandes velocidades, aceleraciones o campos gravitatorios en las tecnologías cuánticas que se avecinan. Aunque a primera vista parece un tema un poco exótico y sin mucha aplicación, lo cierto es que podría ser relevante para los proyectos que planean, en un futuro no muy lejano, usar tecnología cuántica en el espacio. 

A esto, al Lego cuántico y relativista, me dediqué fundamentalmente durante los tres años que trabajé en la Universidad de Nottingham y este es también el núcleo del proyecto "Tecnologías cuánticas 3.0" con el que vuelvo a España (en concreto al Instituto de Física Fundamental del CSIC en Madrid) a dirigir mi propia línea de investigación durante los próximos tres años.  Esto es posible gracias a la primera convocatoria del programa ComFuturo de la Fundación General CSIC, un esquema de colaboración público-privada pionero en España en el que la iniciativa privada financia investigación básica dirigida por jóvenes doctores en centros de investigación públicos

Carlos Sabín Lestayo
Carlos Sabín Lestayo es Investigador del programa ComFuturo en el Instituto de Física Fundamental del CSIC.

Interview: Verónica Fernández Mármol (CSIC)

posted Oct 7, 2015, 8:49 AM by Juan Jose Garcia-Ripoll

Verónica Fernández Mármol
is a young researcher leading a group in experimental Quantum Key Distribution at the Institute of Physical and Information Technologies. Veronica is a member of the Spanish Network in Quantum Information (RICE) and in this interview, she talks about her career paths, the goals of her research and future prospects.

After finishing her degree in Physics in Seville, Verónica Fernández Mármol moved to the UK to do a PhD in experimental QKD at Heriot-Watt University. The topic of her thesis was key distribution using photons that propagate through optical fibers, working in increasing the efficiency and speed at which the random keys are generated. 
In 2007, Verónica returned to Spain, starting a group on experimental QKD but now working with the goal of achieving key distribution through free space, starting with the metropolitan area of Madrid.

Veronica's experiments on quantum cryptography span now a distance of 300 meters, from the Institute of Physical and Information Technologies (CSIC) to a tall building on the neighbouring CSIC campus around the Students Residence in Madrid. In a recent work, her group has demonstrated a high efficiency device, capable of creating private keys at a rate of 1 megabit per second. These are promising results which demonstrate the potential of free space quantum cryptography, and which offers an alternative route to the commercially viable approaches that are pursued by various companies throughout the world (ID Quantique, MagicQ, SeQurenet, ...)

Sketch of the free space quantum cryptography link between Veronica Fernandez's lab (ITEFI) and the emitter node (ICA), separated 300m.

Before entering into the details of your research, could you perhaps explain how and why you entered the field of quantum key distribution?

I was interested in the fields of photonics and optics since I did my degree in Physics but I had little knowledge of Quantum Information specifically. However, as soon as I visited the lab where I later did my PhD in, at Heriot Watt University, I was impressed: finding experimental applications of theoretical principles of fundamental physics such as the Heisenberg Uncertainty Principle was extremely interesting.  Fortunately I could attend some lectures from postgraduate courses that were given in Heriot-Watt University and it helped me improve my background in the field.  Finding a PhD was relatively easy. I just contacted my professor via email, which I got from the University website and he got in touch with me. The demand for postgraduate students in UK is high. My PhD was funded through The Engineering and Physical Sciences Research Council (EPSRC) which is a public organism from the UK specialized in funding research in physical and engineering areas. 

How was the experience of doing a PhD in a foreign university? Did it involve a cultural shock? Did you profit from it in some way? Or has the foreign PhD complicated your life bureaucracy-wise afterwards?

It was a very enriching experience, both from a professional and a personal point of view. Of course, there are cultural differences and it takes some time to adapt but Scotland is a very welcoming country and the level of the research carried out there is very high so I was tremendously lucky to have been given the opportunity to work there. Paper wise, it took me so much time validating my PhD thesis from a Spanish University when I came back, but other than that I didn’t have any problems.

Your work at Heriot Watt University was centered on improving the efficiency of key distribution in optical fibers. What is the present status of this technology? Does it have enough viability to be of commercial interest?

We investigated the approach of using a shorter wavelength, 850 nanometers, for the photon source of a QKD fibre-based system (instead of 1550 nanometers, more commonly employed in fibre-based QKD systems). This wavelength can be efficiently detected by silicon single-photon detectors, which enabled higher rates of operation compared to other single-photon detectors (InGaAs/InP), typically used for detecting 1550 nanometers. Of course a shorter wavelength like 850 nanometers incurs in more losses as it travels through standard telecommunication fiber in the transmission channel but despite this for shorter ranges (20 kilometers) enabled orders of magnitude higher secure key rates than systems working with 1550 nanometers and InGaAs/InP detectors. A few years later, InGaAs/InP detectors were dramatically improved and this approach of using a shorter wavelength is not necessary anymore. 

In 2007 you return to Spain to work on free space quantum key distribution. What does “free space” mean in this context?

Free space means that the stream of photons that travels from Alice to Bob is not guided by physical means, such as optical fibre, but instead travels ‘freely’ through air.

Why “free space”? What are the advantages of not using optical fibres?

There are several advantages of using free space: the first is its strategic role in enabling global quantum communications, which, in a scenario where the practical use of quantum repeaters is, presumably, still far in the horizon, is the only means of leapfrogging the distance limitation imposed by absorption in optical fibres.

Another important advantage is its role in metropolitan networks, where the key advantage of free space links is the installation flexibility they offer due to their portability: they can be relocated in different places according to the needs of the network. The ease and speed of installation is also important, especially in scenarios of natural catastrophes or military conflicts, for example, where the installation of optical fibre might be damaged or impaired. It can also be used as a means to increase the bandwidth of specific points in the network affected by poor connectivity.

And what about the new challenges introduced by free space quantum communication? What are the problems solved by your research?

Secure key rates of quantum communication remains low. We have worked in trying to improve this for free-space QKD links in urban areas. The main challenges to achieve this are: an emitter and receiver capable of operating at very high speeds. In our case the emitter operates at clock frequencies of GHz, for which timing jitters of all electronic equipment must be kept extremely low (a few picoseconds). At the same time filtering solar radiation off your detectors is another challenge, especially in daylight, since the background light from the sun is coupled into the detectors increasing the error. Nevertheless, we achieved secret key rates higher than similar systems. However, improving the stability of the link by beam tracking techniques can increase key rates even more and this is the line we are investigating now: strategies to compensate for atmospheric turbulent effects.

Can you explain a bit how your QKD device works?

It consists of two modules: a transmitter and a receiver. The transmitter uses three lasers: two for the quantum signal and a third for a reference clock that serves for timing synchronization of both stations. The three lasers are directed to two lenses that expand and collimate the beam to be sent to the receiver. The receiver is composed of a Schmidt-Cassegrain telescope with the QKD receiver attached. The received events are measured with a high precision electronic card attached to a PC and are used to analyze the quantum bit error rate of the transmission and thus its security.

Receiver and emitter for the free space QKD scheme developed by Veronica's group.

Various groups in Europe and China are pursuing quantum communication using ground-to-satellite links. Could you tell us a bit about this effort and how this relates to your research?

Using satellites as relay stations can solve the distance-limitation problem that quantum communications faces. China did some very important experimental tests like launching a bright stream of photons to an orbiting satellite and measuring the reflected (single photon) signal back to earth, simulating a satellite sending a single-photon stream to ground. They are also planning on launching a spacecraft in 2016, called the Chinese Quantum Science Satellite, specifically designed to test these concepts.

This year, European researchers from the University of Padova have managed to recover the information of polarization-encoded photons after being sent and reflected from different orbiting satellites and demonstrated that the quantum bit error rate can be kept low enough to perform quantum communications. This is crucial for the future of quantum satellite communications. So progress in the field is continuous.

Our work is more focused on shorter-links applications for metropolitan networks, and improving its speed.

There seem to be two major approaches to the distribution of quantum keys. One method is the BB84 protocol which sends individual photons with random polarization from one device to another. The other alternative is to generate a pair of entangled photons and send them to the two parties which want to generate the key. In both cases, the random orientation of the photon polarization and of the measurement basis ensures secrecy and security. What are the advantadges of each method? Which one do you or your colleagues use?

There are two main QKD schemes: the prepare-and-measure protocols which use mainly polarized photons (WCP) and entanglement-based QKD, which uses entangled photons. The first is based on quantum uncertainty whereas the second is on quantum entanglement. Each has different advantages and disadvantages. For example entanglement based QKD can in principle tolerate more losses (up to 70dB) than WCP-based protocols, although technologically speaking the process of efficiently generating entangled pairs can be more challenging. We use the first approximation.

What is the position of Spain in the fields of quantum communication and quantum cryptography? Do you feel that experimental quantum information is sufficiently represented in our country, or how could this be improved?

There are excellent theoretical and experimental groups dedicated to quantum information technologies in Spain, but comparatively-speaking, our critical mass is still below countries like United Kingdom, France or Germany. I think quantum technologies is already a key field that is taking a major role in fields like security, computation, sensors, biomedicine, etc., and this dominance will presumably increase over the next few years. Most countries have realized this and are investing accordingly in this field. Spain should do the same or we will miss this train.

How does experimental science fare in our science system? Is it very expensive to set up an experiment like the one you are conducting? Can it be done with just national funds?

Experimental science is usually more costly than theoretical fields and requires more resources: human and technical and therefore in a country not used to invest largely in scientific fields it tends to be more difficult to get funding’s. However, it is possible and our laboratory was funded with national projects from previous calls (2008-2012) and internal funds from strategic plans from CSIC.

On a related topic, your situation as a woman leading a group in experimental physics is still quite rare in our science system. Do you feel that we still have a long way to go regarding gender equality in our field? Can we do anything about this?

Indeed. We still have a long road in educating young girls in the fields of science and engineering since numbers of woman conducting science or technical careers are still low. And even more worrying figures are shown by a still high number of women leaving the field after having children. I believe this is a consequence of the absence of conciliation programs in Spain as well as impossible working schedules, which stems from a wrong mentality of companies regarding productivity based more on hours spent at work instead of accomplished objectives.

Finally, what are your next challenges? Do you intend to increase the distance at which your device operates, or does it need a major redesign to do so?

We are working on implementing beam tracking techniques for our QKD system. Beam tracking stabilizes the received beam from the random ‘dancing’ due to atmospheric effects such as beam wander, which provokes random deflections of the beam as it propagates through the transmission channel. This has its origin in random movements or air masses at different temperature causing unpredictable fluctuations of air’s refraction index. This can be compensated for with a configuration that includes fast steering mirrors and position sensitive detectors. Compensating this effect will enable higher secure key rates and longer distances.

Interview: Antonio Acín (ICFO)

posted Aug 31, 2015, 1:27 AM by Juan Jose Garcia-Ripoll

Quantum Mechanics is the nightmare of science communicators. The apparent obscurity of its rules and the unintuitive nature of many of its results often lead to articles where the words “spooky”, “multiverse” or “conscience” substitute for simpler, less mystical explanations that emphasize the utilitarian aspects of this theory. Antonio Acín, leader of a big research group at the Institute of Photonics (ICFO) in Catalonia, works both on Quantum Information Theory, a field of Physics that cares both about the theory behind quantum mechanical systems and their application to tasks in information processing, computation or even materials design. He is also a good communicator who, through many popular talks and writings, helps a wider audience understand those unintuitive aspects of Quantum Mechanics that, one day, could have a practical implication in their lives.

One of Antonio Acin’s research interests is Quantum Cryptography or, more precisely, Quantum Key Distribution, a process by which two parties, Alice and Bob, create and share a secret string of bits with which they can encode messages and communicate securely. There are many methods to do QKD, one of which is to share an entangled state of two physical systems, one of which is sent to Alice and the other one to Bob. Because of entanglement, when both Alice and Bob measure their physical systems in the same way, the outcome of those measurements are perfectly correlated: for example, if Alice measures the polarization of the photon and the outcome is “left” or “right”, she can predict the result of Bob’s measurement (typically the opposite one, “right” and “left”). This way they can share a string of measurement outcomes (bits), which is random and can act as a shared secret key to encode messages. A crucial point in this respect is the secret nature of this key: if third parties intercept their measurements, change their state and attempt to influence their measurement outcomes, Alice and Bob can detect it.

At the core of Quantum Key Distribution's security is the fact that measurement outcomes in Quantum Mechanics are random, and our description of the microscopic nature is probabilistic. Nowadays this randomness is also seen as a resource that can be used for generating better keys that can power encryption and communication mechanisms, not only with quantum algorithms, but also at the classical level, engineering random number generators that are used by ordinary computers and classical devices.

You have both an education as a physicists and as an engineer. When and how did you get interested in Quantum Information?

In 1997, after getting my two degrees in Physics and Telecommunication Engineering, I knew I wanted to go for a PhD in Physics but I did not know the topic yet. I decided to take the PhD courses and look for an interesting research topic in the meantime. Then, Anna Sanpera and Ignacio Cirac gave a (I think two-week) course on quantum information theory at the Faculty of Physics of the University of Barcelona and I immediately understood that I had found the topic I was looking for.

Quantum Cryptography has always seemed the most viable commercial application of Quantum Information in the short term. How do you view the field or what is missing for this?

From a scientific point of view, the device-independent approach has opened many new promising perspectives in quantum cryptography, and also new theoretical and experimental challenges. From a commercialisation point of view, quantum cryptography has still to find its place, I guess. However, the Snowden affair has proven that it may be risky to base the security of critical applications on just one approach and it is better to combine many of them (for instance by combining keys generated by different protocols). It is plausible that quantum solutions become one of these cryptographic protocols used to encrypt messages.

Your work on QKD has always had a leg on foundational aspects of Quantum Mechanics. More recently you have worked on “device-independent” protocols to assert the security of QKD devices. Roughly, it seems that one would design an apparatus for QKD assuming that Quantum Mechanics works and then try to verify that it is secure even if Quantum Mechanics were wrong. Is this right? What are the current implications of this idea?

Yes, I like the device-independent approach because it allows me to study very fundamental questions and, at the same time, think of information protocols to solve relevant problems, such as secure encryption.

While it is possible that the device-indepedent approach may allow us to design protocols that remain secure even if quantum physics was proven to be wrong, this is not my main motivation to study these protocols. Some years ago, there were some successful hacking attacks on quantum cryptography protocols. What the hackers exploited is that the real devices used in the implementation did not work as assumed in the theoretical security proof. This opened a security loophole, which was exploited by the quantum hackers. In the device-independent approach, protocols are defined without any modelling of the devices used in the implementation. Thus, there cannot be any mismatch between what the theoretical security proof demands and what happens in the implementation, as the devices can just be seen as a black box. This device-independent property makes the resulting protocols robust against the existing having attacks. In my view, device-indenpendent protocols define the right avenue for quantum cryptography.

Do you believe in post-quantum theories or do you feel comfortable with the state-of-the-art and how we work with it?

I don’t believe that quantum theory is the final theory, but my experience says that it is very difficult to conceive a reasonable theory beyond quantum physics. Most of my work is on standard quantum physics, but I’m also interested in thinking about how a theory beyond quantum could look like. In fact, I have a recently awarded FQXI project with Miguel Navascués, from the University of Bilkent, whose main goal is to explore some possibilities in this direction.

Your favourite interpretation of Quantum Mechanics?

I don’t have any favourite interpretation, sorry. I guess it is due to my Engineering education...

And how does “randomness” enter the picture? Quantum measurements are supposed to be random but... can we really prove it?

It is impossible to prove randomness from scratch, you always need some assumptions. But in quantum physics, under some mild assumptions, such as the impossibility of faster than light communication, yes, you can certify that a device is random, in the sense that its outcomes are unpredictable. It is hard to digest, I agree, but it is a mathematical fact.

Quantum random number generators: a viable commercial technology?

Difficult to say at the moment. But I think the advantages of using quantum resources are clear, so I’m in principle optimistic.

The issue of randomness also has deep scientific and philosophical implications. This year you organized a conference in Barcelona, Quantum Randomness with a strong interdsiplinary orientation and over 100 participants. Can you briefly comment on the outcome of the conference or its implications for the future?

The idea was to provide a space for interaction for some of the different communities interested in randomness: mathematicians, physicists, engineers and philosophers. The outcome was very positive, and I also got very good feedback from some of the participants.

What about Quantum Engineering? Do you see this also as a viable concept in the near future?

I’m fully convinced that engineers will have to face quantum limits and they will control them. I don’t see any fundamental limitation and to me it seems a natural evolution of the field.

In the mean time, and after supervising 12 thesis, what would be your advice for students that want to initiate themselves into this field? Is Quantum Information still an emergent field or have all the easy questions been already answered?

My advise is that, while Quantum Information may not be an emergent field as some years ago and most of the easy questions have been solved, it is still a nice field for a PhD work that cover many different aspects of science: from very abstract questions to experiments.

You are a strong advocate of scientific outreach, with over 11 talks and four popular science articles. Is the society sufficiently aware of progress in Quantum Information and Technology? Or is the field still too mystified and we need better communicators or a deeper penetration in the media?

I think quantum physics in general is slightly mystified. In my outreach activities, I try to convey that while quantum physics is for sure counter-intuitive, it is less “magic” than what is sometimes said. More in general, I believe scientists should make an effort to reach the general public so that they can make part of our results too.

You supervise a group with over 20 members, half of which are students. How is the daily life in such groups?

My day basically consists of scientific discussions with my group members. But this is one of my favourite activities as a scientist.

Is it difficult to sustain such a big theory group in the present academic and scientific system?

In Spain, it is extremely difficult. But I’m lucky because I got an ERC grant, and ICFO, my institution, and ICREA strongly support my research effort. I also devote a significant amount of time to write proposals and applications for research funding.

Finally, the only question that really matters: Guardiola or Luis Enrique?

Time will tell but I’m afraid I will see no team playing as the Barça of Guardiola.

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