Interferometers operating at or close to quantum limits of precision have found wide application in tabletop searches for physics beyond the standard model, the study of fundamental forces and symmetries of nature and foundational tests of quantum mechanics. The limits imposed by quantum fluctuations and measurement backaction on conventional interferometers (δφ ∼ 1/ √ N ) have spurred the development of schemes to circumvent these limits through quantum interference, multiparticle interactions and entanglement. A prominent example of such schemes, the so-called SU (1, 1) interferometer, has been shown to be particularly robust against particle loss and inefficient detection, and has been demonstrated with photons and ultracold atoms. Here, we realize a SU (1, 1) interferometer in a fundamentally new platform in which the interfering arms are distinct flexural modes of a millimeter-scale mechanical resonator. We realize up to 15.4(3) dB of noise squeezing and demonstrate the Heisenberg scaling of interferometric sensitivity (δφ ∼ 1/N ), corresponding to a 6-fold improvement in measurement precision over a conventional interferometer. Our work extends the optomechanical toolbox for the quantum manipulation of macroscopic mechanical motion and presents new avenues for studies of optomechanical sensing and the nonequilibrium dynamics of multimode optomechanical systems.

We report on micro-focused Raman spectroscopy of encapsulated vanadium tetracyanoethylene (V­[TCNE] x , x ≈ 2) films as they age under ambient conditions to understand the structural changes that accompany aging and how those changes influence the magnetic properties. V­[TCNE] x is an organic-based ferrimagnet with a high magnetic ordering temperature T C > 600 K, low magnetic damping, and growth compatibility with a wide variety of substrates. However, similar to other organic-based materials, it is sensitive to air. Although encapsulation of V­[TCNE] x with glass and epoxy extends the film lifetime from hours to weeks, its aging processes remain poorly understood. We identify the relevant features in the Raman spectra in agreement with ab initio theory, reproducing CC and CN stretching vibrational modes. We correlate changes in the Raman intensity and in photoluminescence to changes in the magnetic properties of the sample as measured using ferromagnetic resonance and magnetometry. Based on changes in the Raman spectra, we hypothesize structural changes and aging mechanisms in V­[TCNE] x . We also find that we can introduce similar changes using focused laser illumination at high intensity, enabling a new mechanism for “erasing” magnetism in this material through selective modification of local bonding. These findings enable a local optical probe of V­[TCNE] x film quality, which is invaluable in experiments where assessing film quality with local magnetic characterization is not possible, and they enable patterning of V­[TCNE] x by laser writing.

Open quantum systems exhibit a range of novel out-of-equilibrium behavior due to the interplay between coherent quantum dynamics and dissipation. Of particular interest in these systems are driven, dissipative transitions, the emergence of dynamical phases with novel broken symmetries, and critical behavior that lies beyond the conventional paradigms of Landau-Ginzburg phenomenology. Here, we consider a parametrically driven two-mode system in the presence of non-Markovian system-reservoir interactions. We show that non-Markovianity modifies the phase diagram of this system resulting in the emergence of a novel broken symmetry phase in a new universality class that has no counterpart in a Markovian or equilibrium system. Such reservoir-engineered dynamical phases can potentially shed light on universal aspects of dynamical phase transitions in a wide range of non-equilibrium systems, and aid in the development of techniques for the robust generation of entanglement and quantum correlations at finite temperatures with potential applications to quantum metrology.

The spectrally narrow, spin-dependent optical transitions of nitrogen vacancy (NV) center defects in diamond can be harnessed for quantum networking applications. Key to such networking schemes is the generation of indistinguishable photons. Two challenges limit scalability in such systems: defect-to-defect variations of the optical transition frequencies caused by local strain variation, and spectral diffusion of the optical frequencies on repeated measurement caused by photoexcitation of nearby charge traps. In this experimental study we undertake a group theoretic approach to quantifying spectral diffusion and strain, decomposing each into components corresponding to Jahn-Teller symmetries of the NV center. We investigate correlations between the components of strain, spectral diffusion, and depth from surface, finding that strain and spectral diffusion are each dominated by longitudinal perturbations. We also find a weak negative correlation between transverse static strain and total spectral diffusion suggesting that transverse strain provides some degree of protection from spectral diffusion. Additionally, we find that spectral diffusion becomes more pronounced with increasing depth in the diamond bulk. Our symmetry-decomposed technique for quantifying spectral diffusion can be valuable for understanding how a given nanoscale charge trap environment influences spectral diffusion and for developing strategies of mitigation.

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