Perturbation-free studies of single molecules

March 12, 2020

Researchers of the University of Basel have developed a new method with which individual isolated molecules can be studied precisely - without destroying the molecule or even influencing its quantum state. This highly sensitive technique for probing molecules is widely applicable and paves the way for a range of new applications in the fields of quantum science, spectroscopy and chemistry, as the journal Science reports.

Spectroscopic analyses are based on the interaction of matter with light and represent the most important experimental tool to study the properties of molecules. In typical spectroscopic experiments, a sample containing a large number of molecules is irradiated directly. The molecules can only absorb light at well-defined wavelengths which correspond to energy differences between two of their quantum states. This is referred to as a spectroscopic excitation.

In the course of these experiments, the molecules are perturbed and change their quantum state. In many cases, the molecules even have to be destroyed to detect the spectroscopic excitations. The analysis of the wavelengths and the intensities of these excitations provide information on the chemical structure of the molecules and their motions such as rotations or vibrations.

Inspired by quantum methods developed for the manipulation of atoms, the research group of Prof. Stefan Willitsch at the Department of Chemistry of the University of Basel has developed a new technique which enables spectroscopic measurements on the level of a single molecule, here as an example a single, charged nitrogen molecule. The new technique does not disturb the molecule or even perturb its quantum state.

In their experiments, the molecule is trapped in a radiofrequency trap and cooled down to near the absolute zero point of the temperature scale (approx. -273 °C). To enable cooling, an auxiliary atom (here a single, charged calcium atom) is simultaneously trapped and localized next to the molecule. This spatial proximity is also essential for the subsequent spectroscopic study of the molecule.

A single molecule in an optical lattice

Subsequently, a force is generated on the molecule by focusing two laser beams on the particles to form a so-called optical lattice. The strength of this optical force increases with the proximity of the irradiated wavelength to a spectroscopic excitation in the molecule resulting in a vibration of the molecule within the trap instead of its excitation.

The strength of the vibration is thus related to the proximity to a spectroscopic transition and is transmitted to the neighboring calcium atom from which it is detected with high sensitivity. In this way, the same information on the molecule can be retrieved as in a conventional spectroscopic experiment.

This method, which is a new type of force spectroscopy, introduces several new concepts: First, it relies on single molecules instead of large ensembles. Second, it represents a completely non-invasive technique as detection is accomplished indirectly (via a neighboring atom) and without a direct excitation of spectroscopic transitions. Therefore, the quantum state of the molecule is left intact, so that the measurement can be repeated continuously. As a result, the method is much more sensitive than established spectroscopic methods that rely on the direct excitation and destruction of a large number of molecules.

Applications in extremely precise clocks and building blocks for quantum computers

There is a range of prospective applications of the new method, Prof. Willitsch explains: "Our type of force spectroscopy allows extremely precise measurements on molecules which are not possible with conventional spectroscopic techniques. With the new method, one can study molecular properties and chemical reactions in very sensitively and under precisely defined conditions on the single-molecule level. It also paves the way for investigations of very fundamental questions such as ?Are physical constants really constant or do they vary with time?? A more practical application could be the development of an ultraprecise clock based on a single molecule - or the application of molecules as building blocks for quantum computers."

University of Basel

Related Spectroscopy Articles from Brightsurf:

Perspectives of infrared spectroscopy in quantitative estimation of proteins
The present review describes the basic principle and the instrumentation of IR spectroscopy along with its advancements.

A new method to measure optical absorption in semiconductor crystals
Tohoku University researchers have revealed more details about omnidirectional photoluminescence (ODPL) spectroscopy - a method for probing semiconducting crystals with light to detect defects and impurities.

Properties of catalysts studied with gamma ray resonance
Steam-assisted oil extraction methods for heavy deposits have long been the focus of attention at Kazan Federal University.

Researchers demonstrate record speed with advanced spectroscopy technique
Researchers have developed an advanced spectrometer that can acquire data with exceptionally high speed.

Spectroscopy approach poised to improve treatment for serious heart arrhythmia
Researchers have demonstrated that a new mapping approach based on near infrared spectroscopy can distinguish between fat and muscle tissue in the heart.

Late blight research pairs spectroscopy with classic plant pathology diagnostics
Gold and colleagues at the University of Wisconsin-Madison recently published research showing how they used contact spectroscopy to non-destructively sense how plant pathogens differentially damage, impair, and alter plant traits during the course of infection.

Doing more with terahertz: Simplifying near-infrared spectroscopy systems
Researchers from Beihang University, China, and Tokushima University, Japan, have developed a terahertz spectroscopy scheme that offers outstanding resolution using a single laser.

A new horizon for vibrational circular dichroism spectroscopy
(1) The development of solid state and time-step VCD methods opened a new horizon to reveal the mechanism of chirality amplification from microscopic to supramolecular scales.

Unraveling the optical parameters: New method to optimize plasmon enhanced spectroscopy
Plasmon enhanced spectroscopies allow to reach single molecule sensitivity and a lateral resolution even down to sub-molecular resolution.

Nanoscale spectroscopy review showcases a bright future
A new review authored by international leaders in their field, and published in Nature, focuses on the luminescent nanoparticles at the heart of many advances and the opportunities and challenges for these technologies to reach their full potential.

Read More: Spectroscopy News and Spectroscopy Current Events is a participant in the Amazon Services LLC Associates Program, an affiliate advertising program designed to provide a means for sites to earn advertising fees by advertising and linking to