Mechanical modes are a potentially useful resource for quantum information applications, such as quantum-level wavelength transducers, due to their ability to interact with electromagnetic radiation across the spectrum. A significant challenge for wavelength transducers is thermomechanical noise in the mechanical mode, which pollutes the transduced signal with thermal states. In this paper, we eliminate thermomechanical noise in the GHz-frequency mechanical breathing mode of a piezoelectric optomechanical crystal using cryogenic cooling in a dilution refrigerator. We optically measure an average thermal occupancy of the mechanical mode of only 0.7 ± 0.4 phonons, providing a path towards low-noise microwave-to-optical conversion in the quantum regime.Quantum information science may have begun with atoms and optical photons, but it has expanded to include numerous experimental platforms that have demonstrated quantum behavior. Examples of quantum devices now include a wide array of well-controlled natural systems including neutral atoms [1], ions [2, 3], electronic [4,5] and nuclear spins [6,7], as well as fabricated systems such as quantum dots [8], superconducting circuits [9][10][11], and mechanical devices [12][13][14][15]. Each system has a unique set of properties that make them advantageous for specific applications: for example, long coherence times make atomic systems a natural candidate for quantum memories [16][17][18][19], while the flexible nature of fabrication makes superconducting circuitry ideal for creating quantum processing gates [20]. This has culminated in the vision of hybrid quantum systems that can link multiple sub-systems into complex quantum machines [21,22].One major challenge in creating hybrid quantum systems arises from transferring quantum information between the different sub-systems. Photons are the obvious medium for transferring of information as most quantum systems can interact with light, however the relevant wavelength varies widely. Furthermore, quantum information has been effectively transferred over long distances using optical photons [23][24][25]. This has spurred interest in the development of mechanical wavelength transducers -devices that use photon-phonon interactions to coherently convert photons between different wavelengths while preserving quantum information. In particular, interest lies in converting between the microwave frequencies used in superconducting quantum processors and telecom-wavelength optical photons used in fiber networks for the purposes of networking quantum processors [21]. At its core, a mechanical wavelength transducer consists of a mechanical element coupled to two electromagnetic resonances at the desired input/output wavelengths. State-of-the-art transducers have demonstrated wavelength conversion for classical signals within the optical wavelength range [26][27][28], within the microwave regime [29,30], the up-conversion of microwave tones to optical wavelengths [31][32][33], and the bidirectional conversion of microwave and optical si...

Cavity optomechanics has demonstrated remarkable capabilities, such as measurement and control of mechanical motion at the quantum level. Yet many compelling applications of optomechanics—such as microwave-to-telecom wavelength conversion, quantum memories, materials studies, and sensing applications—require hybrid devices, where the optomechanical system is coupled to a separate, typically condensed matter, system. Here, we demonstrate such a hybrid optomechanical system, in which a mesoscopic ferromagnetic needle is integrated with an optomechanical torsional resonator. Using this system we quantitatively extract the magnetization of the needle, not known a priori, demonstrating the potential of this system for studies of nanomagnetism. Furthermore, we show that we can magnetically dampen its torsional mode from room-temperature to 11.6 K—improving its mechanical response time without sacrificing torque sensitivity. Future extensions will enable studies of high-frequency spin dynamics and broadband wavelength conversion via torque mixing.

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A polygonal chain is the union of a finite number of straight line segments in ℝ3 that are connected end-to-end. Two chains are considered to be equivalent if there is an isotopy of ℝ3 that moves one chain to the other while keeping the segments rigid. Each segment must remain straight during the isotopy and the lengths of the segments may not change, but bending and twisting are allowed at the joints between the segments. Chains may be knotted and stuck in this category even though all chains are topologically trivial. Cantarella and Johnston have classified polygonal chains with five or fewer segments. In this paper we classify polygonal chains of six segments.

A wide variety of applications of microwave cavities, such as measurement and control of superconducting qubits, magnonic resonators, and phase noise filters, would be well served by having a highly tunable microwave resonance. Often this tunability is desired in situ at low temperatures, where one can take advantage of superconducting cavities. To date, such cryogenic tuning while maintaining a high quality factor has been limited to ∼ 500 MHz. Here we demonstrate a three-dimensional superconducting microwave cavity that shares one wall with a pressurized volume of helium. Upon pressurization of the helium chamber the microwave cavity is deformed, which results in in situ tuning of its resonant frequency by more than 5 GHz, greater than 60% of the original 8 GHz resonant frequency. The quality factor of the cavity remains approximately constant at ≈ 7 × 10 3 over the entire range of tuning. As a demonstration of its usefulness, we implement a tunable cryogenic phase noise filter, which reduces the phase noise of our source by approximately 10 dB above 400 kHz.Three dimensional (3D) microwave cavities have proven to be an indispensable part of many quantum systems. They have recently been used in conjunction with superconducting qubits 1 to make spectacular progress in the field of cavity QED, where they are integral components in the implementation of universal gate sets, 2 nondestructive measurement of single microwave photons, 3 and implementation of programmable interference between quantum memories. 4 When paired with ferromagnetic spheroids, 5 they readily exhibit strong coupling to spin resonances, 6,7 which has allowed for the field of cavity magnonics to flourish with applications such as bidirectional microwave-optical conversion 8 and resolving magnon number states. 9 When coupled to a mechanical element, such as a membrane 10 or superfluid helium, 11 they form an optomechanical system with the potential for exceedingly high cooperativities and quality factors, allowing for the rich toolbox of optomechanics to be employed.In all of these applications, cryogenic tunability of the microwave cavity -without sacrificing the quality factor (Q)would allow for the use of superconducting materials, desirable for the high quality factors they confer. For instance, one can imagine a superconducting qubit encapsulated inside a superconducting resonator. Normally, such a qubit is tuned by the application of a magnetic field, 12 but this is prohibited inside a superconducting cavity due to field exclusion from the Meissner effect. With a highly-tunable cavity, one could enjoy all the advantages of a superconducting cavity while still being able to control its detuning with respect to a qubit. Similarly for cavity magnonics, a highly-tunable cavity could allow control of the phonon-magnon hybridization without the need for a tunable magnetic field.In addition to their uses outlined above, microwave cavities are useful in both classical and quantum systems as phase noise filters. [13][14][15] Classically, phase noise...