Reversing the direction of heat flow using quantum correlations (1711.03323v2)

Abstract: Heat spontaneously flows from hot to cold in standard thermodynamics. However, the latter theory presupposes the absence of initial correlations between interacting systems. We here experimentally demonstrate the reversal of heat flow for two quantum correlated spins-1/2, initially prepared in local thermal states at different effective temperatures, employing a Nuclear Magnetic Resonance setup. We observe a spontaneous energy flow from the cold to the hot system. This process is enabled by a trade off between correlations and entropy that we quantify with information-theoretical quantities. These results highlight the subtle interplay of quantum mechanics, thermodynamics and information theory. They further provide a mechanism to control heat on the microscale.

• The paper demonstrates that introducing quantum correlations in qubit systems can invert the traditional flow of heat from hot to cold.
• Using an NMR setup and quantum state tomography, the researchers measured energy shifts and mutual information changes to validate theoretical predictions.
• The study highlights that quantified non-classical correlations, via geometric quantum discord, can enable innovative microscale thermal management.

Reversing the Direction of Heat Flow Using Quantum Correlations

The paper "Reversing the direction of heat flow using quantum correlations" presents an experimental investigation into the role of quantum correlations in reversing the traditional thermodynamic heat flow direction. This work leverages quantum information theory principles to challenge the classical assumption that heat naturally flows from hot to cold systems. The paper employs a Nuclear Magnetic Resonance (NMR) setup to explore how quantum correlations between qubits can reverse this conventional direction.

Key Experimental and Theoretical Insights

The experiment detailed in the paper involves two spin-1/2 systems (qubits) correlated quantum mechanically, each initially in local thermal states but at different effective temperatures. The authors utilize a NMR setup to manipulate and measure the system, meticulously tracking the heat exchange and correlation dynamics over time. Through quantum state tomography, they gather empirical data validating theoretical conjectures about quantum thermodynamics.

A pivotal theoretical result explored is the breakdown of the classical heat flow from hot to cold and the conditions under which heat can flow inversely. Quantum correlations introduce a mutual information dynamic that allows, under certain conditions, for heat to spontaneously flow from the colder system to the hotter one, contradicting classical thermodynamic proclivities. This reversal is facilitated by the non-classical reduction of mutual information, offsetting entropy production traditionally associated with spontaneous processes.

Numerical and Empirical Assertions

The researchers report specific numerical changes in internal energy and mutual information that highlight this phenomenon. In the uncorrelated scenario, measured heat flows align with the second law of thermodynamics, confirming hot-to-cold energy transfer. In contrast, when initiating with quantum correlations, their results—backed by careful statistical analysis and simulations—demonstrate a reversal where energy is transferred from cold to hot.

Furthermore, they quantify the role of geometric quantum discord to identify the degree of quantumness in the initial correlations, revealing that non-zero discord values signal potential for such a reversal. The paper underscores that the mutual information can decrease with time, exploiting quantum resources to manifest this unconventional heat flow.

Implications and Future Directions

This research deepens the understanding of the interplay between quantum mechanics and thermodynamics, specifically in cases involving initial correlations. By experimentally demonstrating that such correlations can dynamically influence entropy and heat exchange directions, the paper lays a foundation for future explorations into microscopic thermal management using quantum systems.

The implications extend into practical applications, particularly in the development of quantum-thermodynamic technologies and microscale heat management. The potential to manipulate heat transfer directionally at quantum scales could revolutionize sectors ranging from quantum computing to nanoscale thermal engineering.

Moving forward, the researchers hint at exploring the scaling effects of their findings. Questions remain about how larger quantum systems could sustain or magnify these observed heat flow reversals and their theoretical bounds. Continued exploration could unveil novel quantum states manipulation techniques, offering greater control over energy distribution and conversion at the smallest scales.

Conclusively, the work presents a significant contribution to the discourse on the quantum thermodynamics frontier, expanding theoretical and practical horizons with its empirically-backed insights into non-classical heat interactions.