New strategy reveals 'full chemical complexity' of quantum decoherence

The results can be used to design molecules with customized quantum coherence properties, laying the chemical foundation for emerging quantum technologies.

In quantum mechanics, particles can exist in multiple states at the same time, defying the logic of everyday experiments. This property, known as quantum superposition, is the basis for emerging quantum technologies that promise to transform computing, communications, and sensing. But quantum superpositions face a major challenge: quantum incoherence. During this process, the precise superposition of quantum states collapses when interacting with its surrounding environment.

The challenge of quantum decoherence

To unleash the power of chemistry to build complex molecular structures for practical quantum applications, scientists need to understand and control quantum decoherence so they can design molecules with specific quantum coherence properties. Doing so requires knowing how to rationally modify the chemical structure of the molecule to modify or relax quantum bonding. To this end, scientists need to know “spectral density,” a quantity that summarizes how fast the environment is moving and how strongly it interacts with the quantum system.

A breakthrough in spectral density measurement

Until now, measuring this spectral density in a way that accurately reflects the complexities of molecules has remained theoretically and experimentally elusive. But a team of scientists has developed a way to extract the spectral density of molecules in solvents using simple resonance Raman experiments, a method that captures the full complexity of chemical environments. Led by Ignacio Franco, associate professor of chemistry and physics at the University of Rochester, the team published their findings in a journal Proceedings of the National Academy of Sciences.

Linking molecular structure to quantum decoherence

Using the extracted spectral density, it is possible not only to understand how quickly debonding occurs, but also to determine which part of the chemical environment is mostly responsible for it. As a result, scientists can now map decoherence pathways to link molecular structure with quantum decoherence.

“Chemistry arises from the idea that molecular structure determines the chemical and physical properties of matter. This principle guides the modern design of molecules for medicine, agriculture, and energy applications. Using this strategy, we can finally begin to develop Chemical design principles for emerging quantum technologies.

Resonance Raman experiments: a key tool

This breakthrough came when the team realized that Raman resonance experiments had yielded all the information needed to study debonding with full chemical complexity. Such experiments are routinely used to study photophysics and photochemistry, but their utility in quantum decoherence has not been appreciated. Key ideas emerged from discussions with David McCamant, an associate professor in the Department of Chemistry at the University of Rochester and an expert in Raman spectroscopy, and with Chang-Woo Kim, now a faculty member at Chonnam National University in Korea and an expert in quantum decoherence, while he was a post- PhD in Rochester.

Case study: Thymine debonding

The team used their method to show, for the first time, how the electron configurations in thymine, one of the basic elements in building… DNAIt disintegrates in only 30 femtoseconds (one femtosecond is one millionth of a billionth of a second) after absorbing ultraviolet radiation. They found that some vibrations in the molecule dominate the initial steps in the debonding process, while the solvent dominates the later stages. In addition, they discovered that chemical modifications to thymine can dramatically change the rate of debonding, with hydrogen bonding interactions near the thymine ring leading to faster debonding.

Implications and future applications

Ultimately, the team's research opens the way toward understanding the chemical principles that govern quantum decoherence. “We are excited to use this strategy to understand quantum decoherence in molecules of full chemical complexity and use it to develop molecules with strong cohesive properties,” says Franco.

Reference: “Mapping electronic debonding paths in molecules” by Ignacio Justin, Chang-Woo Kim, David W. McCamant, and Ignacio Franco, 28 November 2023, Proceedings of the National Academy of Sciences.
doi: 10.1073/pnas.2309987120