China

In many current experimental setups and quantum information technologies, protocols that maximize a case-specific figure of merit are highly desirable. In this talk we focus on the preparation of cat states, i.e., quantum superposition of two opposite-phase coherent states, in a nonlinear optical Kerr resonator. To solve this quantum state control problem, we implement the dynamics of the system as part of a fully differentiable program [1]. This framework ultimately combines machine learning and the knowledge of the differential equations governing the dynamics of the physical system. We employ a neural network that maps the state of the system at a given time to a control pulse. Finally, we verify the robustness of the method against noise in the initial states.

[1] F. Schäfer, M. Kloc, C. Bruder, N. Lörch, Mach. Learn.: Sci Technol. 1 035009

Quantum 2020

A differentiable programming method for optimal preparation of cat states

cat states

scientific machine learning

quantum control

The Institute of Physics and IOP Publishing, in partnership with the Chinese Physical Society (CPS) and the University of Science and Technology of China (USTC) are proud to have brought together the international quantum science community online for this inaugural conference.


Early career and leading researchers from universities, industry and government worldwide came together to share, learn and collaborate on the latest research and emerging areas of high interest across quantum science and technology. The broad themes covered by Quantum 2020 included:

Quantum communication;
Quantum computing and quantum simulation;
Quantum sensing, metrology and imaging;
Quantum information theory, software and algorithms;
Quantum foundations;
Quantum technology in industry.
The four-day event featured talks from world-renowned scientists, interactive poster sessions and two exciting panel discussions on the themes of Quantum Technology in Industry and Quantum Technology Programmes Around the World.


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The Institute of Physics and IOP Publishing, in partnership with the Chinese Physical Society (CPS) and the University of Science and Technology of China (USTC) are proud to have brought together the international quantum science community online for this inaugural conference.

Early career and leading researchers from universities, industry and government worldwide came together to share, learn and collaborate on the latest research and emerging areas of high interest across quantum science and technology. 

poster

In High Energy Physics (HEP), calorimeter outputs play an essential role in understanding low distance processes occurring during particle collisions. Due to the complexity of underlying physics, the traditional Monte-Carlo simulation is computationally expensive, and thus, the HEP community has suggested Generative Adversarial Networks (GAN) for fast simulation. Meanwhile, it has also been proposed that, in certain circumstances, simulation using GANs can itself be sped-up by using quantum GANs (qGANs).
Our work presents an advanced prototype of qGAN, that we call the dual-Parameterized Quantum Circuit (PQC) GAN, with a classical discriminator and two quantum generators which take the form of PQCs. The first PQC learns the probability distribution over the images of N pixels, while the second generates normalized pixel intensities of an individual image for each PQC input. The dual-PQC architecture exhibits an apparent quantum advantage, by using only O(log(N)) qubits, unlike the classical GAN with O(N) neurons. Its performance has been evaluated through the application in HEP to imitate calorimeter outputs, translated into pixelated images. The results demonstrate that the model can reproduce a fixed number of images with a reduced size as well as their probability distribution and allows us to scale up to real calorimeter outputs. 


Dual-Parameterized Quantum Circuit GAN Model in High Energy Physics

In oblivious transfer, a sender Alice sends two bits to a receiver Bob, who only receives one of them. Alice does not know which bit Bob received. Oblivious transfer is a useful cryptographic primitive. It is universal for multiparty computation, where two or more parties want to compute something together, while not revealing more than necessary about their input data to the other party. Perfect quantum oblivious transfer is impossible, but imperfect variants remain possible. We show that it is possible to “reverse” a quantum oblivious transfer protocol by Amiri et al., arXiv:2007.04712, so that one can achieve quantum oblivious transfer “both ways” even if one of the parties can only send quantum states, and the other one can only measure quantum states. This can be useful for applications.


Reversing quantum oblivious transfer

1-2 Oblivious Transfer is a cryptographic primitive in which a sender holds two bits, and a receiver receives one of them in such a way that the receiver does not learn both bits, and the sender does not know which of the bits the receiver has obtained. Perfect Quantum Oblivious Transfer is not possible, but it is possible to have protocols where cheating probabilities for the parties are bounded. Previous
research has found security bounds of 2=3 for general and 0:749 for symmetric pure quantum states. Here we examine a series of incomplete protocols, which means protocols with inherent probability for errors, that allow for security against the sender by no-signalling without allowing the receiver to cheat with unity success probability.
We characterise all incomplete protocols using symmetric states and compare dierent examples for implementable protocols with particular focus on the use of coherent states. Easiest to implement is a protocol in which classical bit value pairs are mapped to four phases +,-,+i,-i of a coherent state, which are distinguished using a single homodyne detection measurement. We show that using single photon BB84 like states provides better performance in terms of security than our coherent state protocols.

Imperfect quantum oblivious transfer where the sender cannot cheat

Photon interference and bunching are widely studied quantum effects that have also been proposed for high-precision measurements. We construct and use a theoretical description of photon interferometry on rotating
platforms, specifically exploring the relation between noninertial motion, relativity, and quantum mechanics. We propose an experiment testing these relations where photon entanglement can be revealed or concealed solely by controlling the rotational motion of an interferometer.

Revealing and concealing entanglement with noninertial motion

The Google announcement of the first experimentally achieved result of the so-called quantum supremacy, based on exploiting the multiqubit entanglement to the problem of randomness verification [https://doi.org/10.1038/s41586-019-1666-5], attracted attention to the classically ungrasped nature of the randomness itself and its verification. The elusive infiniteness of true randomness correlating with the quantum entanglement of the infinite number of entangled qubits asks for a fundamental description. We proposed a simplistic theoretical concept linking the multiqubit entanglement with the randomness in the public patent application in 2017 [PCT/PL2017/000133-WO/2019/132679] and in Sci. Rep. in 2020 [https://doi.org/10.1038/s41598-019-56706-2], the latter coincided in time with Google team announcement. We show that on the theoretical level, the presented concepts are equivalent in the fundamental sense. We discuss our quantum multiqubit entanglement based protocol for quantum random number generation, with unique features, like secure public randomness testing, overcoming local computational restrictions, or arbitrarily diminishing of the average time of the complex randomness testing of finite length bit sequence at the cost of multi-qubit entanglement level. Here, the randomness of the generated single sequence proves the randomness of all the other simultaneously generated sequences (or the randomness of the shorter sequence proves the randomness of longer sequence), which is a crucial result based on the multiqubit quantum entanglement.

Multiqubit entanglement for public randomness testing vs Google's quantum supremacy

The initial research undertaken was aimed at examining the feasibility of adapting and implementing Topological Data Analysis (TDA) methods using Persistent Homology to meet requirements in the telecom domain. Persistent Homology based methods are especially useful in detecting anomalies in time series data and show good prospects of being useful in telecom network alarm data. Here, the special interest to this technique is a metric called the Wasserstein Distance, which shows how much two persistence diagrams correspondingly differ from one another. Calculating this metric is a minimum weight maximum matching problem on a bipartite graph. Existing classical methods of calculating the Wasserstein distance show polynomial time complexity O(n power 3).
We carried out a quantum study which involved converting this Wasserstein matching problem into a Quadratic Unconstrained Binary Optimization problem and minimizing it using a Quantum Annealer approach.
Our final focus on the TDA Wasserstein distance problem is the implementation of an alternate Combinatorial Optimization Quantum Algorithm which should theoretically be faster than existing classical methods, potentially yielding a quantum speedup in detecting anomalies in the future.

Quantum Topological Data Analysis for Anomaly Detection

The violation of seminal Bell-type inequalities in spin polarization correlation experiments stimulated speculations about quantum magic and nonlocality. Some authors claim that the quantum correlations are due to some instantaneous influences between distant quantum systems, that an individual quantum system may be at the same time here and a meter away or that the experimenters’ free will is an illusion. The narrative about the quantum magic is not only grounded in some failed attempts of providing more detailed description of quantum phenomena but also in the disturbing fact that there is no consensus about the interpretation of quantum theory. Nevertheless if one starts talking about magic this is the end of the science. Robert Griffith and several other authors came recently to the conclusion that the quantum nonlocality and the quantum steering are misleading notions which should be abandoned or renamed . The quantum correlations between the outcomes of real experiments with entangled physical systems are strong but imperfect and they can be explained in a locally causal way. it is not true that the entangled systems behave as pairs of fair dice showing always the same outcomes. The important message for quantum information community is that qubits are not the attributes of individual physical systems which can be changed instantaneously by the measurements performed on distant entangled partners.

Demystifying quantum nonlocality

The effect of photon-pair generation rate on quantum entanglement is analyzed.
Two techniques of producing polarization entanglement are compared: a continuously pumped spontaneous parametric down-conversion (SPDC) and a biexciton decay in a quantum dot. We made a comparison of the reconstructed entangled states in terms of performance under device-independent quantum key distribution. We found that the secure key rate of down-converted photon pairs is limited to 0.029 bits per detection window due to intrinsic multiphoton contributions. We also report that there exists one optimum gain for continuous-wave down-conversion sources. We find a bound for secure key rate extracted from SPDC sources and show that quantum dot sources can surpass them with future advancement of their capabilities.


Effect of source statistics on utilizing photon
entanglement in quantum key distribution

Long-lived quantum coherences detected in the Fenna-Matthews-Olson (FMO) light-harvesting complex have ignited the hunt for realistic models that can explain such dynamics. The extraordinary ~100% efficiencies presented by these complexes, operating under noisy environmental conditions, make them an important target for understanding and replicating their success in other practical applications. Despite the experimental developments, computer simulations are needed to perform a true approximation to understand the complex interactions that govern this system. Several methods have been explored to model this quantum phenomenon, mainly based on the quantum open systems theory. The evolution of approaches to the problem has gone from traditional methods which wouldn't consider the memory effects of the surroundings to more robust non-Markovian methods for the modelling of the system evolution with a better representation of environmental interactions. While quantum walks have proven to provide a mathematical framework for the study of energy transfer efficiency in the FMO complex, further characterization of operating conditions may lead to effective control and optimization of the system. We perform a parametric analysis about some physical features in the quantum regime involved during the quantum excitation process to get a comprehension about its non-trivial dependence on operation parameters. Thus, the analysis is conducted in terms of some relevant physical parameters in the system to track the complex global behavior in aspects as coherence, entanglement, decoherence times, transference times, and efficiency of the main process of energy capturing. As a complementary analysis from the derived outcomes, we compare those features for two different species as a suggestive possible roadmap to track genetic differences in the photosynthetic performance of the complex through its biological nature.

Quantum phenomena on life systems: a parametric deep view on the Fenna-Mathews-Olson complex

A variable behaving as a quantum in economic system is studied on the basis of quantum mechanics. The several formulas of relevant variable are derived along with this speculation. Thus a possible value for the common constant which may be understood as Planck constant in economic system is calculated. There, a concerned variable seems to exhibit a quantum behavior.
Recently it has been pointed out that there might be a similarity between the rational expectation hypothesis in economics and quantum mechanics, where their observers are both in respective systems. Nevertheless, on the other hand, the principle of uncertainty in economics has not yet been discovered so far. Therefore we will study on this problem by starting to formulate the basic equations respective which correspond to quantum mechanics. Here we pursue solely a behavior of certain representative variable with which an important econophysical quantity is newly introduced, and then discuss about Planck constant in economic system.


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A differentiable programming method for optimal preparation of cat states

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