Quantum optomechanics of lossy bodies: General approach and structured squeezed vacuum effects

We investigate the overall optomechanical force experienced by a macroscopic lossy object in free space under external quantum illumination. To this end, utilizing the modified Langevin noise formalism, we derive the time-averaged expectation value of the Maxwell stress tensor for a nonequilibrium scenario in which the incoming scattering field is prepared in an arbitrary mixed quantum state, while the medium-assisted field is maintained in local thermal equilibrium. In the limit of full radiation-matter thermal equilibrium, our expression exactly recovers the well-known fluctuation-dissipation relation governing the Casimir effect, and under coherent illumination it yields the standard classical radiation pressure. We demonstrate that by driving the scattering field with an anisotropic, multimode squeezed vacuum state, the spatial profile of the electromagnetic quantum fluctuations can be engineered to exhibit broken rotational symmetry, thereby inducing a fluctuation-driven mechanical force acting on the object. Such mechanical interaction is generated in the strict absence of a mean field 〈 E ̂ 〉 = 0 and is governed exclusively by second-order field correlations 〈 E ̂ 2 〉 , unlike classical optical radiation pressure dictated by the squared mean field 〈 E ̂ 〉 2 . Applying this exact formulation to a homogeneous lossy sphere, we demonstrate the experimental feasibility of the effect using realistic material parameters and optical estimations. Ultimately, we establish a general formalism for macroscopic quantum optomechanics that operates beyond the constraints of thermal equilibrium, enabling the prediction of regimes where the structured force operates without classical carriers, providing a theoretical framework to systematically investigate the mitigation of radiation-pressure shot noise and macroscopic spatial decoherence.