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Gradient Echo Quantum Memory in Warm Atomic Vapor

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Published on: November 11, 2013

Optimal performance of reciprocating demagnetization quantum refrigerators.

Ronnie Kosloff¹, Tova Feldmann

¹Institute of Chemistry, The Hebrew University, Jerusalem 91904, Israel.

Physical Review. E, Statistical, Nonlinear, and Soft Matter Physics

|September 28, 2010

Summary

Quantum refrigerators face limitations in reaching absolute zero due to noise. Uncontrollable energy gaps and control noise prevent perfect adiabatic following, establishing a minimum achievable temperature above absolute zero.

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Area of Science:

Quantum Thermodynamics
Quantum Refrigeration
Statistical Mechanics

Background:

Quantum refrigerators utilize demagnetization and magnetization cycles.
Achieving absolute zero (0 Kelvin) is a fundamental challenge in thermodynamics.
Adiabatic processes are crucial for ideal cooling cycles.

Purpose of the Study:

To investigate the theoretical limitations of cooling to absolute zero using a quantum refrigerator.
To determine the impact of energy gaps and control noise on minimum achievable temperatures.
To analyze the role of non-adiabatic dynamics and quantum friction in cooling cycles.

Main Methods:

Modeling a reciprocating quantum refrigerator based on an Otto cycle with an interacting spin system.
Analyzing the demagnetization and magnetization stages considering an energy gap and control noise.
Defining and applying an adiabatic measure to characterize Hamiltonian changes and deriving closed-form solutions.

Main Results:

An uncontrollable energy gap and control noise lead to a minimum achievable temperature (Tc(min)) above absolute zero.
Noise prevents adiabatic following during demagnetization, causing non-adiabatic dynamics linked to quantum friction.
Frictionless cycles minimizing entropy production can achieve Tc=0, but are eliminated by external noise.

Conclusions:

Quantum refrigerators with noisy controls and energy gaps cannot reach absolute zero.
The minimum temperature is directly influenced by the size of the energy gap and the level of control noise.
External noise fundamentally restricts the ultimate cooling performance of quantum refrigerators.