Cooling-by-measurement and mechanical state tomography via pulsed optomechanics

Abstract

Observing a physical quantity without disturbing it is a key capability for the control of individual quantum systems. Such back-action-evading or quantum-non-demolition measurements were first introduced in the 1970s in the context of gravitational wave detection to measure weak forces on test masses by high precision monitoring of their motion. Now, such techniques have become an indispensable tool in quantum science for preparing, manipulating, and detecting quantum states of light, atoms, and other quantum systems. Here we experimentally perform rapid optical quantumnoise-limited measurements of the position of a mechanical oscillator by using pulses of light with a duration much shorter than a period of mechanical motion. Using this back-action evading interaction we performed both state preparation and full state tomography of the mechanical motional state. We have reconstructed mechanical states with a position uncertainty reduced to 19 pm, limited by the quantum fluctuations of the optical pulse, and we have performed 'cooling-by-measurement' to reduce the mechanical mode temperature from an initial 1100 K to 16 K. Future improvements to this technique may allow for quantum squeezing of mechanical motion, even from room temperature, and reconstruction of non-classical states exhibiting negative regions in their phase-space quasi-probability distribution.Experiments are now beginning to investigate nonclassical motion of massive mechanical devices [1][2][3]. This opens up new perspectives for quantum-physics enhanced applications and for tests of the foundations of physics. A versatile approach to manipulate mechanical states of motion is provided by the interaction with electromagnetic radiation, typically confined to microwave or optical cavities. Such cavity-optomechanics experiments [4][5][6][7][8] have thus far largely concentrated on high sensitivity continuous monitoring of the mechanical position [9][10][11][12][13][14]. Because of the back-action imparted by the probe onto the measured object, the precision of such a measurement is fundamentally constrained by the standard quantum limit (SQL) [15,16], and therefore only allows for classical phase-space reconstruction [9,17,18]. In order to observe quantum mechanical features that are smaller than the mechanical zero-point motion, backaction-evading measurement techniques that can surpass the SQL [19,20] are required. Following the early insights of Braginsky, beating the standard quantum limit 'can be achieved only in one way: design the probe so it "sees" only the measured observable ' [15]. Such backaction evading techniques were first realized for the detection of optical quadratures [21][22][23] and have since been used for, e.g. precision measurement of atomic ensemble spin [24][25][26][27][28] and quantum non-demolition microwave photon counting [29]. In optomechanics, to perform a back-action evading measurement of the mechanical position, a time-dependent measurement scheme is required. One prominent example is the so-called 'two-tone app...

Engineering single-phonon number states of a mechanical oscillator via photon subtraction

“…We have argued that, at variance with a previously reported scheme for the achievement of non-classical mechanical states [11], a dynamical approach with a time-gated photon-subtraction event, and a working point deep in the blue-detuning regime allow for the achievement of the best performances. Once engineered through the protocol illustrated herein, the mechanical state can be reconstructed using high-precision all-optical methods [34,35]. The proposal is thus fully within the reach of current stateof-the-art experiments in optomechanics, and paves the way to a novel approach towards the engineering of key non-Gaussian states of massive mechanical systems and their use for the quantum coherent communication.…”

Optimal quantum parameter estimation in a pulsed quantum optomechanical system

“…For the pulsed optomechanical system, there exist at least two experimentally feasible schemes to achieve this aim. The main idea of the first one [51] is based on the homodyne detection of the mixing between the signal pulses, which interact with the mechanical resonator, and the local oscillator (LO) pulses, as shown in Ref. [51] (wherein Fig.…”

“…Compared with the CW-laser-driving case, the benefit of the pulsed scheme is that it does not need the existence of a stable steady-state for the optomechanical system. The pulsed interaction has also displayed its superiority in preparation and reconstruction of quantum state of the mechanical resonator [46,47], enhancing the optomechaical entanglement [48,49] and EPR steering [50], and cooling the mechanical mode [51,52].…”

“…Inspired by the experimental progress in pulsed quantum optomechanical systems [42,49,51], it is a natural idea to investigate the high precision of parameter estimation by applying applicable optical pulsed driving on the cavity of the optomechanical system. Here we investigate a special pulsed optomechanical system, where the coupling between the mechanical mode and cavity field is quadratical to the mechanical motion and the cavity field is resonantly driven with external optical pulses.…”

Measurement-Induced Macroscopic Superposition States in Cavity Optomechanics

“…Mechanical non-Gaussian states can also be generated in the much simpler bad cavity regime (where the sidebands are unresolved) by using a broadband cavity and either single photon [22] or coherent state resources [23]. However, these protocols rely on an extremely strong non-Gaussian interaction between light and mechanics and are thus of limited practical feasibility due to the insufficient optomechanical interaction strengths currently achievable.As suggested in recent works [24][25][26][27], quantum nondemolition (QND) state transfer [28,29] induced by pulsed optomechanical interaction [30][31][32] offers a more feasible route. Extending this framework, we propose a novel squeezing-enhanced protocol for preparation of macroscopic…”