In quantum mechanics, there is an important concept called quantum coherence, which refers to the superposition of two or more possible states of a quantum system. This superposition state can produce some very wonderful phenomena, such as interference, quantum computing, etc. You can think of quantum coherence as a coin, which is neither heads nor tails, but a mixture of the two, and only when you look at it does it "collapse" into a definite result.
However, quantum coherence is not eternal, it fades away over time, a process called quantum decoherence. Quantum decoherence is caused by the interaction of a quantum system with its surroundings, which destroys the purity and information of the quantum system. You can think of quantum decoherence as a coin that, as it spins in the air, it is collided with air molecules, which changes its state of motion, and finally stops and shows a definite result.
Quantum decoherence is a very important problem in quantum mechanics, which limits the development of quantum technology and hinders our understanding of quantum phenomena. Therefore, we need to find out the causes and mechanisms of quantum decoherence, and how to control and reduce its effects. This is the main content of the ** that we are going to share today, which proposes a method that can be used to analyze and quantify the electron decoherence path in a molecule, i.e., the different factors that lead to the loss of electron coherence.
The method is based on resonance Raman spectroscopy, a spectroscopic technique that can measure vibrational modes in molecules. When a laser beam hits a molecule, it is absorbed or scattered by the molecule, changing its frequency and intensity. These changes reflect the movement of electrons and nuclei in the molecule, which is the vibrational mode of the molecule. By analyzing these vibrational modes, we can obtain the spectral density of the molecule, which is a function that describes the intensity of the molecule's interaction with light.
Spectral density can tell us not only the structure and properties of a molecule, but also the rate of decoherence of a molecule, which is a function that describes the rate of loss of coherence of a molecule. The rate of decoherence determines the coherence time of the molecule. The longer the coherence time, the more pronounced the quantum behavior of the molecule, and the shorter the coherence time, the more ambiguous the quantum behavior of the molecule.
The innovation of this article is that it can not only extract the decoherence rate from the spectral density, but also decompose the decoherence rate into different decoherence paths, i.e., different factors that cause decoherence. These factors include the vibrational patterns inside the molecule, as well as the interaction of the molecule with the solvent. By analyzing these decoherence pathways, we can find out which factors contribute the most to decoherence and how to regulate decoherence by changing the structure or environment of the molecule.
The results of this article are based on a common molecule, thymine, which is a base in DNA and a fundamental building block of life. The authors measured the spectral density of thymine and its derivatives in water by resonance Raman spectroscopy, and extracted the decoherence rate and decoherence pathway from it. They found that the electronic coherence of thymine disappeared in about 30 femtoseconds, which is a very short time. They also found that the main factor leading to decoherence is the vibrational mode within the molecule, especially the vibrational mode related to the electron transition, while the interaction between the molecule and the solvent has a smaller effect on the decoherence.
In addition, they found that by altering the structure of thymine, such as adding or removing certain atoms or groups, the decoherence rate and decoherence path can be significantly altered. For example, the rate of decoherence increases when there is a hydrogen atom on the ring of thymine that forms a hydrogen bond with water, whereas when there is a methyl group substituted hydrogen atom on the ring of thymine, the rate of decoherence decreases. These results suggest that the structure and chemical properties of molecules have an important impact on decoherence, and also provide us with a possible way to regulate decoherence.