Organic molecule fluorescence as an experimental test-bed for quantum jumps in thermodynamics

Cormac Browne,Vedral Vlatko,Robert A Taylor,Tristan Farrow,Oscar C O Dahlsten

doi:10.1098/rspa.2017.0099

Abstract

We demonstrate with an experiment how molecules are a natural test bed for probing fundamental quantum thermodynamics. Single-molecule spectroscopy has undergone transformative change in the past decade with the advent of techniques permitting individual molecules to be distinguished and probed. We demonstrate that the quantum Jarzynski equality for heat is satisfied in this set-up by considering the time-resolved emission spectrum of organic molecules as arising from quantum jumps between states. This relates the heat dissipated into the environment to the free energy difference between the initial and final state. We demonstrate also how utilizing the quantum Jarzynski equality allows for the detection of energy shifts within a molecule, beyond the relative shift.

Highlights

Marrying the language of thermodynamics with quantum phenomena is giving rise to a quantum thermodynamics whose development defines a new frontier where the transfer of energy at the level of individual quantum objects can be studied
Our result provides an important proof of concept for the validity of quantum thermodynamics in this regime, and opens the door for more advanced tests of the theory
We examine the spectroscopic data from spontaneous emission of the organic molecule DBT in an anthracene crystal

Summary

Introduction

Marrying the language of thermodynamics with quantum phenomena is giving rise to a quantum thermodynamics whose development defines a new frontier where the transfer of energy at the level of individual quantum objects can be studied. It is becoming possible to study energy transfers at the level of single-molecules, some of which offer ideal test-beds owing to their well-defined spectroscopic signatures and quantum state dynamics Their properties are extremely reproducible, more so than rival quantum systems such as quantum dots and nanocrystals [25,26]. The system offers an ideal experimental test bed that is robust, readily available and accessible to infrared spectroscopy, presenting an energy level structure with atom-like sharp two-level transitions typical of organic fluorescent dyes despite the relative complexity of the molecules Their chemical structure consists of corrugated planar assemblies of aromatic hydrocarbons (figure 2a) that dopes anthracene via two insertion sites, or defects, in the extended crystal lattice, giving rise to two distinct spectral lines at λ ∼ 785 nm and 795 nm at cryogenic temperatures. We probe the brighter blue-shifted site emitting at 785 nm

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