Buffoni L, Gherardini S, Zambrini Cruzeiro E, Omar Y. Third Law of Thermodynamics and the Scaling of Quantum Computers.
PHYSICAL REVIEW LETTERS 2022;
129:150602. [PMID:
36269957 DOI:
10.1103/physrevlett.129.150602]
[Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/11/2022] [Revised: 08/31/2022] [Accepted: 09/01/2022] [Indexed: 06/16/2023]
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.
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