Laser cooling a membrane-in-the-middle system close to the quantum ground state from room temperature

Many protocols in quantum science and technology require initializing a system in a pure quantum state. In the context of the motional state of massive resonators, this enables studying fundamental physics at the elusive quantum–classical transition, and measuring force and acceleration with enhanced sensitivity. Laser cooling has been a method of choice to prepare mechanical resonators in the quantum ground state, one of the simplest pure states. However, to overcome the heating and decoherence by the thermal bath, this usually has to be combined with cryogenic cooling. Here, we laser-cool an ultracoherent, soft-clamped mechanical resonator close to the quantum ground state directly from room temperature. To this end, we implement the versatile membrane-in-the-middle setup with one fiber mirror and one phononic crystal mirror, which reaches a quantum cooperativity close to unity already at room temperature. We furthermore introduce a powerful combination of coherent and measurement-based quantum control techniques, which allows us to mitigate thermal intermodulation noise. The lowest occupancy we reach is 30 phonons, limited by measurement imprecision. Doing away with the necessity for cryogenic cooling should further facilitate the spread of optomechanical quantum technologies

The “Roll and Lock” Mechanism of Force Generation in Muscle

SummaryMuscle force results from the interaction of the globular heads of myosin-II with actin filaments. We studied the structure-function relationship in the myosin motor in contracting muscle fibers by using temperature jumps or length steps combined with time-resolved, low-angle X-ray diffraction. Both perturbations induced simultaneous changes in the active muscle force and in the extent of labeling of the actin helix by stereo-specifically bound myosin heads at a constant total number of attached heads. The generally accepted hypothesis assumes that muscle force is generated solely by tilting of the lever arm, or the light chain domain of the myosin head, about its catalytic domain firmly bound to actin. Data obtained suggest an additional force-generating step: the “roll and lock” transition of catalytic domains of non-stereo-specifically attached heads to a stereo-specifically bound state. A model based on this scheme is described to quantitatively explain the data

MAGNETIC NANOCOMPOSITES BASED ON MAGNETITES AND BIOPOLYMERS

By precipitation of ammonia from a mixed aqueous solution of FeCl2 and FeCl3 in a stoichiometric ratio of 1:2, magnetite particles were synthesized, magnetic flocculants were obtained by mixing them with natural polysaccharides, and their flocculating properties were analyzed.Работа выполнена при финансовой поддержке Министерства науки и высшего образования Российской Федерации в рамках государственного задания на оказание государственных услуг (проект № 075-01508-23-00), Фонда содействия инновациям в рамках гранта «Студенческий стартап» 3-я очередь СтС-307197 и Благотворительного фонда Владимира Потанина

Entanglement between Distant Macroscopic Mechanical and Spin Systems

Entanglement is a vital property of multipartite quantum systems, characterised by the inseparability of quantum states of objects regardless of their spatial separation. Generation of entanglement between increasingly macroscopic and disparate systems is an ongoing effort in quantum science which enables hybrid quantum networks, quantum-enhanced sensing, and probing the fundamental limits of quantum theory. The disparity of hybrid systems and the vulnerability of quantum correlations have thus far hampered the generation of macroscopic hybrid entanglement. Here we demonstrate, for the first time, generation of an entangled state between the motion of a macroscopic mechanical oscillator and a collective atomic spin oscillator, as witnessed by an Einstein-Podolsky-Rosen variance below the separability limit, $0.83 \pm 0.02<1$. The mechanical oscillator is a millimeter-size dielectric membrane and the spin oscillator is an ensemble of $10^9$ atoms in a magnetic field. Light propagating through the two spatially separated systems generates entanglement due to the collective spin playing the role of an effective negative-mass reference frame and providing, under ideal circumstances, a backaction-free subspace; in the experiment, quantum backaction is suppressed by 4.6 dB. Our results pave the road towards measurement of motion beyond the standard quantum limits of sensitivity with applications in force, acceleration,and gravitational wave detection, as well as towards teleportation-based protocols in hybrid quantum networks.Comment: 24 pages, 12 figure