The third law of thermodynamics, also known as the Nernst unattainability principle, puts a fundamental bound on how close a system, whether classical or quantum, can be cooled to a temperature near to absolute zero. On the other hand, a fundamental assumption of quantum computing is to start each computation from a register of qubits initialized in a pure state, i.e., at zero temperature. These conflicting aspects, at the interface between quantum computing and thermodynamics, are often overlooked or, at best, addressed only at a single-qubit level. In this Letter, we argue how the existence of a small but finite effective temperature, which makes the initial state a mixed state, poses a real challenge to the fidelity constraints required for the scaling of quantum computers. Our theoretical results, carried out for a generic quantum circuit with N-qubit input states, are validated by test runs performed on a real quantum processor.

Third Law of Thermodynamics and the Scaling of Quantum Computers / Buffoni, Lorenzo; Gherardini, Stefano; Zambrini Cruzeiro, Emmanuel; Omar, Yasser. - In: PHYSICAL REVIEW LETTERS. - ISSN 0031-9007. - ELETTRONICO. - 129:(2022), pp. 150602-150608. [10.1103/PhysRevLett.129.150602]

Third Law of Thermodynamics and the Scaling of Quantum Computers

Buffoni, Lorenzo
;
Gherardini, Stefano;
2022

Abstract

The third law of thermodynamics, also known as the Nernst unattainability principle, puts a fundamental bound on how close a system, whether classical or quantum, can be cooled to a temperature near to absolute zero. On the other hand, a fundamental assumption of quantum computing is to start each computation from a register of qubits initialized in a pure state, i.e., at zero temperature. These conflicting aspects, at the interface between quantum computing and thermodynamics, are often overlooked or, at best, addressed only at a single-qubit level. In this Letter, we argue how the existence of a small but finite effective temperature, which makes the initial state a mixed state, poses a real challenge to the fidelity constraints required for the scaling of quantum computers. Our theoretical results, carried out for a generic quantum circuit with N-qubit input states, are validated by test runs performed on a real quantum processor.
2022
129
150602
150608
Buffoni, Lorenzo; Gherardini, Stefano; Zambrini Cruzeiro, Emmanuel; Omar, Yasser
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Utilizza questo identificatore per citare o creare un link a questa risorsa: https://hdl.handle.net/2158/1306160
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