[Paper Review] Observation of optomechanical buckling phase transitions

Haitan Xu, Utku Kemiktarak+4 more|arXiv (Cornell University)|Oct 16, 2015

Mechanical and Optical Resonators3 citations

TL;DR

This paper reports the first experimental observation of radiation-pressure-induced buckling phase transitions in an optomechanical system, where laser power and detuning drive first- and second-order transitions between stable mechanical states. The system exhibits symmetry-broken phases with a membrane's displacement as the order parameter, validated by quantitative agreement with a theoretical phase diagram.

ABSTRACT

Correlated phases of matter provide long-term stability for systems as diverse as solids, magnets, and potential exotic quantum materials. Mechanical systems, such as relays and buckling transition spring switches can yield similar stability by exploiting non-equilibrium phase transitions. Curiously, in the optical domain, observations of such phase transitions remain elusive. However, efforts to integrate optical and mechanical systems -- optomechanics -- suggest that a hybrid approach combining the quantum control of optical systems with the engineerability of mechanical systems may provide a new avenue for such explorations. Here we report the first observation of the buckling of an optomechanical system, in which transitions between stable mechanical states corresponding to both first- and second-order phase transitions are driven by varying laser power and detuning. Our results enable new applications in photonics and, given rapid progress in pushing optomechanical systems into the quantum regime, the potential for explorations of quantum phase transitions.

Motivation & Objective

• To observe optomechanical buckling phase transitions driven by radiation pressure, a phenomenon predicted decades ago but previously unobserved in the optical domain.
• To demonstrate controlled transitions between stable mechanical states in a symmetric Fabry-Perot cavity with a dielectric membrane, using laser power and detuning as tuning parameters.
• To establish a phase diagram for optomechanical buckling, linking optical driving conditions to mechanical stability and symmetry breaking.
• To explore the potential of optomechanical systems for classical and quantum information processing through robust, switchable mechanical states.
• To validate theoretical models of optomechanical phase transitions by comparing predicted and measured transition points in the parameter space of laser power and detuning.

Proposed method

• Utilized a symmetric Fabry-Perot cavity with a suspended silicon nitride membrane as the mechanical resonator, enabling independent control of optical and mechanical properties.
• Employed two independent tunable lasers (1560 nm) with electro-optic phase modulators to generate pump and probe fields, enabling precise control of laser detuning and power.
• Applied the Pound-Drever-Hall technique to lock the pump fields to cavity modes and use the beat signal between probe lasers as a sensitive readout of membrane displacement.
• Used high-frequency counter and PDH signal analysis to measure membrane position variations across different bandwidths, enabling detection of static and dynamic mechanical states.
• Conducted finite element analysis to simulate mechanical modes and optimize the tethered membrane design for low effective spring constant and enhanced optical spring effects.
• Developed a theoretical model of the optomechanical potential, showing a transition from single-well to multi-well potential with increasing optical power, leading to phase transitions.

Experimental results

Research questions

• RQ1 Can radiation pressure induce first- and second-order phase transitions in a symmetric optomechanical system with a dielectric membrane?
• RQ2 How does the optical driving power and detuning control the transition between stable mechanical states in an optomechanical cavity?
• RQ3 To what extent does the system exhibit spontaneous symmetry breaking during the buckling transition, and how does this differ from asymmetric bistability?
• RQ4 What is the quantitative agreement between the theoretical phase diagram and experimental observations of transition points?
• RQ5 How do high-frequency mechanical modes and thermal effects influence the observed phase transitions and stability?

Key findings

• The first experimental observation of optomechanical buckling phase transitions was achieved, with transitions between stable mechanical states driven by laser power and detuning.
• Both first- and second-order phase transitions were observed, with the membrane's displacement serving as the order parameter and symmetry breaking occurring at the transition point.
• The experimental phase diagram showed good quantitative agreement with theory, particularly in the locations of critical transition points for varying laser detuning and power.
• The system exhibited a smooth transition from a single-well to a double-well potential as optical power increased, confirming the theoretical basis for the phase transitions.
• The use of a symmetric cavity enabled spontaneous symmetry breaking, contrasting with earlier asymmetric systems like the Dorsel experiment.
• Despite challenges from high-frequency mechanical modes and thermal heating, the observed behavior remained consistent with theory, especially in the low-bandwidth regime.