Physical limits of heat-bath algorithmic cooling.

Area of Science:

• Quantum Information Science
• Quantum Computing Hardware
• Thermodynamics of Quantum Systems

Background:

• Achieving ground-state initialization for qubits is a fundamental challenge in quantum computing.
• Existing closed-system cooling methods are insufficient due to ancilla requirements and high initial temperatures.
• Open-system cooling mechanisms are necessary for practical quantum computing architectures.

Purpose of the Study:

• To present a novel and efficient initialization procedure for open quantum systems.
• To demonstrate near-perfect qubit state preparation from a maximally mixed state.
• To establish theoretical limits for quantum state initialization.

Main Methods:

• Development of a new open-system initialization protocol.
• Analysis of qubit initialization in contact with a biased heat bath.
• Investigation of a critical threshold effect in quantum cooling.

Main Results:

• The proposed procedure achieves almost perfect initialization for an n-qubit device with a heat bath bias epsilon >> 2^(-n).
• A newly discovered threshold effect demonstrates optimal performance is achievable.
• For bias epsilon << 2^(-n), significant initialization is fundamentally impossible, even in principle.

Conclusions:

• The developed open-system initialization procedure offers an efficient solution for preparing qubits in their ground states.
• The findings highlight a fundamental threshold limiting the effectiveness of quantum cooling and initialization.
• This work advances the practical realization of fault-tolerant quantum computing by addressing a key initialization hurdle.