Browsing by Subject "Quantum Physics"
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Item Nano-welding of quantum spin-1/2 chains at minimal dissipation(2024-04-15) Cavalcante, M. F.; Bonança, Marcus V. S.; Miranda, Eduardo; Deffner, SebastianWe consider the optimal control of switching on a coupling term between two quantum many-body systems. Specifically, we (i) quantify the energetic cost of establishing a weak junction between two quantum spin-1/2 chains in finite time τ and (ii) identify the energetically optimal protocol to realize it. For linear driving protocols, we find that for long times the excess (irreversible) work scales as τ−η, where η=1,2 or a nonuniversal number depending on the phase of the chains. Interestingly, increasing a Jz anisotropy in the chains suppresses the excess work thus promoting quasi-adiabaticity. The general optimal control problem is solved, employing a Chebyshev ansatz. We find that the optimal control protocol is intimately sensitive to the chain phases.Item Quantum Computing: Vision and Challenges(2024-03-04) Gill, Sukhpal Singh; Cetinkaya, Oktay; Marrone, Stefano; Combarro, Elias F.; Claudino, Daniel; Haunschild, David; Schlote, Leon; Wu, Huaming; Ottaviani, Carlo; Liu, Xiaoyuan; Machupalli, Sree Pragna; Kaur, Kamalpreet; Arora, Priyansh; Liu, Ji; Shamshad, Salman; Farouk, Ahmed; Song, Houbing; Uhlig, Steve; Ramamohanarao, KotagiriThe recent development of quantum computing, which makes use of entanglement, superposition, and other quantum fundamental concepts, has the ability to provide substantial processing advantages over traditional computing. These quantum features help solve many hard problems that cannot be solved with traditional computing methods. These problems are in areas like modeling quantum mechanics, logistics, making chemical-based advances, designing drugs, statistical science, sustainable energy, banking, reliable communication, and quantum chemical engineering. The last few years have witnessed remarkable advancements in quantum software and algorithm creation as well as quantum hardware research, which have significantly advanced the prospect of the realization of quantum computers. It would be helpful to have comprehensive literature research on this area to grasp the current status and find outstanding problems that require considerable attention from the research community working in the quantum computing industry. To better understand quantum computing, this paper examines the foundations and vision based on current research in this area. We discuss cutting-edge developments in quantum computer hardware advancement, and subsequent advances in quantum cryptography, quantum software, and high-scalability quantum computers. Many potential challenges and exciting new trends for quantum technology research and development are highlighted in this paper for a wider debate.Item Quantum speed limit for Kirkwood-Dirac quasiprobabilities(2024-02-12) Pratapsi, Sagar Silva; Deffner, Sebastian; Gherardini, StefanoWhat is the minimal time until a quantum system can exhibit genuine quantum features? To answer this question we derive quantum speed limits for two-time correlation functions arising from statistics of measurements. Generally, these two-time correlators are described by quasiprobabilities, if the initial quantum state of the system does not commute with the measurement observables. Our quantum speed limits are derived from the Heisenberg-Robertson uncertainty relation, and set the minimal time at which a quasiprobability can become non-positive, which is evidence for the onset of non-classical traits in the system dynamics. As an illustrative example, we apply these results to a conditional quantum gate, by determining the optimal condition giving rise to non-classicality at maximum speed. Our analysis also hints at boosted power extraction in genuinely non-classical dynamics.