Directly observing squeezed phonon states with femtosecond x-ray diffraction.

Area of Science:

• Condensed matter physics
• Quantum optics
• Materials science

Background:

• Squeezed states represent quantum states with reduced uncertainty in conjugate variables.
• Ultrafast optical excitation can induce squeezed phonon states in crystalline materials.
• Phonon squeezing arises from transient changes in interatomic bonding.

Purpose of the Study:

• To experimentally measure squeezing oscillations in phonon states.
• To investigate the impact of electronic excitation on phonon modes.
• To validate theoretical models of light-matter interaction in crystals.

Main Methods:

• Femtosecond X-ray diffraction was employed to probe atomic dynamics.
• Ultrafast optical pulses were used to excite crystalline bismuth.
• Analysis focused on measuring oscillations in atomic displacements.

Main Results:

• Squeezing oscillations were successfully measured in bismuth.
• The observed oscillations align with theoretical predictions.
• Results indicate a consistent softening of all phonon modes.

Conclusions:

• Electronic excitation in bismuth leads to the creation of squeezed phonon states.
• A model where electronic excitation uniformly softens phonon modes is supported.
• Femtosecond X-ray diffraction is a viable technique for studying transient quantum phenomena.