[Paper Review] Matter-wave physics with nanoparticles and biomolecules

Christian Brand, Sandra Eibenberger+2 more|arXiv (Cornell University)|Mar 6, 2017

Mechanical and Optical Resonators4 citations

TL;DR

This paper presents experimental and theoretical advances in matter-wave interferometry with large organic molecules and biomolecules, demonstrating quantum interference of complex systems up to 10,000 amu. It details techniques for generating slow, beam-sorted neutral biomolecular beams using laser desorption and electrospray ionization, enabling quantum optics with peptides and proteins in near-field interferometers, achieving high-precision metrology and probing quantum delocalization in biologically relevant matter.

ABSTRACT

These lecture notes emerged from a contribution to the "Les Houches Summer School, Session CVII - Current Trends in Atomic Physics, July 2016". It is meant to serve students as a guide to a selection of topics that are currently at the focus of molecular quantum optics and complements an earlier lecture on related topics [Arndt et al., 2014]. In this review we discuss recent advances in molecular quantum optics with large organic molecules. In particular, we present successful experiments of molecules of biological importance, such as neurotransmitters and map out the route towards interferometry of large bio-matter such as proteins. The interaction of internally complex molecules with various beam splitters is discussed for both far-field diffraction at a single nanomechanical grating and the Kapitza-Dirac Talbot-Lau near-field interferometer - addressing recent progress, experimental challenges, and prospects for quantum enhanced metrology of highly complex systems in the gas phase. A central part of this review deals with the preparation of slow beams of neutral biomolecules, ranging from a single amino acid to proteins or peptides in a micro-environment.

Motivation & Objective

• To extend matter-wave interference experiments to highly complex, biologically relevant molecules such as peptides and proteins.
• To address the challenge of preparing slow, mass-selected beams of neutral biomolecules in the 10^3–10^6 amu mass range.
• To develop and apply near-field interferometers, particularly Kapitza-Dirac-Talbot-Lau interferometers, for probing quantum superposition in large molecules.
• To enable quantum-enhanced metrology of biomolecular structure and dynamics using matter-wave interference.
• To explore the limits of quantum coherence in macroscopic, thermally excited, internally complex systems.

Proposed method

• Utilizes laser-induced acoustic desorption and laser injection into noble gas beams to generate thermal beams of large peptides.
• Employs electrospray ionization (ESI) to produce highly charged biomolecules, followed by charge reduction via collisions in bi-polar air and mass selection in a quadrupole filter.
• Applies cryogenic buffer gas cooling in hexapole guides to reduce internal and translational temperature of mass-selected molecules.
• Uses photo-depletion gratings in a near-field interferometer setup to coherently split and recombine matter waves of large molecules.
• Employs a Kapitza-Dirac-Talbot-Lau interferometer (KDTLI) with optical phase gratings to achieve high-contrast interference patterns.
• Combines theoretical modeling of decoherence and quantum dynamics with experimental validation using time-of-flight mass spectrometry.

Experimental results

Research questions

• RQ1 Can quantum superposition and interference be observed in molecules as large and complex as proteins (up to 10,000 amu)?
• RQ2 What are the dominant decoherence mechanisms affecting matter-wave interference in thermally excited, internally complex biomolecules?
• RQ3 How can neutral beams of large biomolecules be generated with sufficient intensity, velocity control, and mass selection for quantum interferometry?
• RQ4 To what extent can quantum interference enhance the precision of biomolecular metrology?
• RQ5 What are the prospects for observing quantum effects in systems like viruses or hydrated biomolecules using matter-wave interferometry?

Key findings

• Interference patterns have been experimentally observed for large organic molecules exceeding 10,000 amu, demonstrating quantum delocalization in massive, complex systems.
• Electrospray ionization enables the production of highly charged biomolecules (e.g., myoglobin at 17,000 amu), which are subsequently cooled and mass-selected for interferometry.
• Charge reduction techniques via collisions in bi-polar air reduce the charge-to-mass ratio to values suitable for beam transport and interferometry (e.g., 1,000–2,000 amu/e).
• The Kapitza-Dirac-Talbot-Lau interferometer achieves high-contrast interference fringes with large molecules, confirming coherent matter-wave splitting and recombination.
• Photo-depletion gratings have been developed as a promising method for generating coherent beam splitters in near-field interferometry, though still under active investigation.
• Theoretical models confirm that internal degrees of freedom and environmental interactions are key sources of decoherence, which must be minimized for macroscopic superpositions.