Search

Quantum computers are here, and the search for applications and use of these allow us to overcome the limits that today's hardware information processing gives us is constantly going on. Quantum machine learning is one of the many emerging fields that use quantum computers to process information. In this paper, we present a method and a set of experiments where we see the potential and capacity of the Noisy intermediate-scale quantum hardware for the execution of different models having as the basis in some of them the quantum algorithm corresponding to the Quantum Fourier Transform. With this, we demonstrate the effectiveness of how this algorithm can enhance the performance of quantum computations in quantum machine learning models in near-term applications. We used the systems offered by IBM Quantum and the cross-platform Python library for quantum differentiable programming Pennylane by Xanadu Quantum Technologies Inc. [ABSTRACT FROM AUTHOR]

In quantum information, the qubit is not represented by a full spinor in space and in time as the z spinor below: Ψ0(z) = (2πσ20)-12e-z24σ20(cosθ02e-iϕ02sinθ02eiϕ02) but by a simplified spinor without spatial extension Ψ = (cosθ02e-iϕ02sinθ02eiϕ02) This simplification is the basis of our first criticism of the quantum computer concept. Indeed, the demonstrations explaining the interest of the Deutsch, Glover and Shor algorithms are based on calculations using the factorization of entangled qubits. These factorizations are accurate for spinors without spatial extensions, but only approximate for real spinors with spatial extensions. Through the spatial extension question, we also revisit the Stern and Gerlach experiment, to explain the decoherence, the individual impacts and the quantization. We conclude in two other criticism what this spin interpretation implies for the feasibility of quantum computers. A second, more fundamental criticism concerns the existence of the (single) spin-based qubit itself. Indeed, we show that the variables of space and spin are not factorizable duringmeasurement. It seems that the qubit, which is a simplified spinor, does not exist as individual object, at least during the measurement. A third criticism deals with the completness of quantum mechanics. Our analysis explains very simply the negative results of the NMR technique, developed by Chuang et al, which does not use quantum objects individually. The spinor spatial extension takes into account the initial position z0 of the particle. [ABSTRACT FROM AUTHOR]

Can we reduce Quantum Field Theory (QFT) to a quantum computation? Can physics be simulated by a quantum computer? Do we believe that a quantum field is ultimately made of a numerable set of quantum systems that are unitarily interacting? A positive answer to these questions corresponds to substituting QFT with a theory of quantum cellular automata (QCA), and the present work is examining this hypothesis. These investigations are part of a large research program on a quantum-digitalization of physics, with Quantum Theory as a special theory of information, and Physics as emergent from the same quantum-information processing. A QCA-based QFT has tremendous potential advantages compared to QFT, being quantum ab-initio and free from the problems plaguing QFT due to the continuum hypothesis. Here I will show how dynamics emerges from the quantum processing, how the QCA can reproduce the Dirac-field phenomenology at large scales, and the kind of departures from QFT that that should be expected at a Planckscale discreteness. I will introduce the notions of linear field quantum automaton and local-matrix quantum automaton, in terms of which I will provide the solution to the Feynman's problem about the possibility of simulating a Fermi field with a quantum computer. [ABSTRACT FROM AUTHOR]

Optical implementations of qubits play an important role for quantum information science. Photons are ideal carriers of quantum information due to low decoherence rates and are easily controllable by standard off-the-shelf components. Over the last decade the degree of control over photonic single- and two-qubit operations has improved substantially, which recently enables the complex state engineering of various multi-photon states. The control of current four- and six-photon entangled states provides access for the investigation of interesting properties of multi-particle entangled states and for overcoming the random nature of spontaneous emission sources. [ABSTRACT FROM AUTHOR]

We apply quantum control techniques to a long spin chain by acting only on two qubits at one of its ends, thereby implementing universal quantum computation by a combination of quantum gates on these qubits and indirect SWAP operations across the chain. It is shown that the control sequences can be computed and implemented efficiently. We discuss the application of these ideas to physical systems such as superconducting qubits in which full control of long chains is challenging. [ABSTRACT FROM AUTHOR]

Spin is a quantum property of electrons. For spin-based quantum information technology, preparation and read-out of the electron spin state should be spin coherent. We demonstrate that the polarization coherence of light can be transferred to the spin coherence of electrons in a semiconductor quantum nanostructure, and the prepared coherence of the electron spin can also be read out with light by the developed tomographic Kerr rotation method. We also demonstrate that a single photon is efficiently converted (∼27%) into a single electron trapped in a gate-defined quantum dot, where the g-factor of electrons is tuned to zero, and the charge state is detected with an adjacent quantum point contact without destructing the spin state. We further demonstrate that the spin coherence of a single electron trapped in one of double quantum dots is electrically manipulated with a microwave applied to the gate and read out via the Pauli spin blockade phenomenon. All of these functions are needed to build all semiconductor quantum repeaters and distributed quantum computers. [ABSTRACT FROM AUTHOR]

Teleportation-based quantum information processing is reviewed. [ABSTRACT FROM AUTHOR]