scholarly journals In situ upgrade of quantum simulators to universal computers

Quantum ◽  
2018 ◽  
Vol 2 ◽  
pp. 80 ◽  
Author(s):  
Benjamin Dive ◽  
Alexander Pitchford ◽  
Florian Mintert ◽  
Daniel Burgarth
Keyword(s):  
Optimal Control ◽  
Control Problem ◽  
Strong Evidence ◽  
Logic Gates ◽  
Quantum Systems ◽  
Quantum Computers ◽  
Quantum Simulators ◽  
Universal Quantum ◽  
Classical Computer

Quantum simulators, machines that can replicate the dynamics of quantum systems, are being built as useful devices and are seen as a stepping stone to universal quantum computers. A key difference between the two is that computers have the ability to perform the logic gates that make up algorithms. We propose a method for learning how to construct these gates efficiently by using the simulator to perform optimal control on itself. This bypasses two major problems of purely classical approaches to the control problem: the need to have an accurate model of the system, and a classical computer more powerful than the quantum one to carry out the required simulations. Strong evidence that the scheme scales polynomially in the number of qubits, for systems of up to 9 qubits with Ising interactions, is presented from numerical simulations carried out in different topologies. This suggests that this in situ approach is a practical way of upgrading quantum simulators to computers.

Non-integrability of the optimal control problem for n-level quantum systems

2017 ◽  
Vol 50 (17) ◽  
pp. 175202 ◽  
Author(s):  
Guillaume Duval ◽  
Andrzej Maciejewski ◽  
Witold Respondek
Keyword(s):  
Optimal Control ◽  
Optimal Control Problem ◽  
Control Problem ◽  
Quantum Systems ◽  
N Level

scholarly journals Quantum Computers as Universal Quantum Simulators: State‐of‐the‐Art and Perspectives

2019 ◽  
Vol 3 (3) ◽  
pp. 1900052 ◽  
Author(s):  
Francesco Tacchino ◽  
Alessandro Chiesa ◽  
Stefano Carretta ◽  
Dario Gerace
Keyword(s):  
State Of The Art ◽  
Quantum Computers ◽  
Quantum Simulators ◽  
Universal Quantum

scholarly journals A quantum Fredkin gate

2016 ◽  
Vol 2 (3) ◽  
pp. e1501531 ◽  
Author(s):  
Raj B. Patel ◽  
Joseph Ho ◽  
Franck Ferreyrol ◽  
Timothy C. Ralph ◽  
Geoff J. Pryde
Keyword(s):  
Quantum Computer ◽  
Logic Gates ◽  
Quantum Systems ◽  
Black Box ◽  
Quantum Computers ◽  
Fredkin Gate ◽  
Swap Gate ◽  
Quantum Analog ◽  
Photonic Qubit ◽  
Qubit Operation

Minimizing the resources required to build logic gates into useful processing circuits is key to realizing quantum computers. Although the salient features of a quantum computer have been shown in proof-of-principle experiments, difficulties in scaling quantum systems have made more complex operations intractable. This is exemplified in the classical Fredkin (controlled-SWAP) gate for which, despite theoretical proposals, no quantum analog has been realized. By adding control to the SWAP unitary, we use photonic qubit logic to demonstrate the first quantum Fredkin gate, which promises many applications in quantum information and measurement. We implement example algorithms and generate the highest-fidelity three-photon Greenberger-Horne-Zeilinger states to date. The technique we use allows one to add a control operation to a black-box unitary, something that is impossible in the standard circuit model. Our experiment represents the first use of this technique to control a two-qubit operation and paves the way for larger controlled circuits to be realized efficiently.

REDUCED MODEL OF PLASMA DISCHARGE CONTROL IN TOKAMAK WITH IRON CORE

2020 ◽  
Vol 7 (3) ◽  
pp. 11-22
Author(s):  
VALERY ANDREEV ◽  
◽  
ALEXANDER POPOV
Keyword(s):  
Optimal Control ◽  
Inverse Problem ◽  
Optimal Control Problem ◽  
Control Problem ◽  
Nonlinear Behavior ◽  
Plasma Discharge ◽  
Reduced Model ◽  
Iron Core ◽  
Power Sources ◽  
Real Power

A reduced model has been developed to describe the time evolution of a discharge in an iron core tokamak, taking into account the nonlinear behavior of the ferromagnetic during the discharge. The calculation of the discharge scenario and program regime in the tokamak is formulated as an inverse problem - the optimal control problem. The methods for solving the problem are compared and the analysis of the correctness and stability of the control problem is carried out. A model of “quasi-optimal” control is proposed, which allows one to take into account real power sources. The discharge scenarios are calculated for the T-15 tokamak with an iron core.

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