arXiv subjects

Hendrik Schütz

Publications and source records attributed to Hendrik Schütz.

3 recordsLinked to original sources

arXiv2016

Appearance and disappearance of quantum correlations in measurement-based feedback control of a mechanical oscillator

Quantum correlations between imprecision and back-action are a hallmark of continuous linear measurements. Here we study how measurement-based feedback can be used to improve the visibility of quantum correlations due to the interaction of a laser field with a nano-optomechanical system. Back-action imparted by the meter laser, due to radiation pressure quantum fluctuations, gives rise to correlations between its phase and amplitude quadratures. These quantum correlations are observed in the experiment both as squeezing of the meter field fluctuations below the vacuum level in a homodyne measurement, and as sideband asymmetry in a heterodyne measurement, demonstrating the common origin of both phenomena. We show that quantum feedback, i.e. feedback that suppresses measurement back-action, can be used to increase the visibility of the sideband asymmetry ratio. In contrast, by operating the feedback loop in the regime of noise squashing, where the in-loop photocurrent variance is reduced below the vacuum level, the visibility of the sideband asymmetry is reduced. This is due to feedback back-action arising from vacuum noise in the homodyne detector. These experiments demonstrate the possibility, as well as the fundamental limits of measurement-based feedback as a tool to manipulate quantum correlations.

quant-ph↗

arXiv2016

Near-field integration of a SiN nanobeam and a SiO$_2$ microcavity for Heisenberg-limited displacement sensing

Placing a nanomechanical object in the evanescent near-field of a high-$Q$ optical microcavity gives access to strong gradient forces and quantum-noise-limited displacement readout, offering an attractive platform for precision sensing technology and basic quantum optics research. Robustly implementing this platform is challenging, however, as it requires separating optically smooth surfaces by $\lesssimλ/10$. Here we describe a fully-integrated evanescent opto-nanomechanical transducer based on a high-stress Si$_3$N$_4$ nanobeam monolithically suspended above a SiO$_2$ microdisk cavity. Employing a novel vertical integration technique based on planarized sacrificial layers, we achieve beam-disk gaps as little as 25 nm while maintaining mechanical $Q\times f>10^{12}$ Hz and intrinsic optical $Q\sim10^7$. The combined low loss, small gap, and parallel-plane geometry result in exceptionally efficient transduction, characterizing by radio-frequency flexural modes with vacuum optomechanical coupling rates of 100 kHz, single-photon cooperativities in excess of unity, and zero-point frequency (displacement) noise amplitudes of 10 kHz (fm)/$\surd$Hz. In conjunction with the high power handling capacity of SiO$_2$ and low extraneous substrate noise, the transducer operates particularly well as a sensor. Deploying it in a 4 K cryostat, we recently demonstrated a displacement imprecision 40 dB below that at the standard quantum limit (SQL) with an imprecision-back-action product $<5\cdot\hbar$. In this report we provide a comprehensive description of device design, fabrication, and characterization, with an emphasis on extending Heisenberg-limited readout to room temperature. Towards this end, we describe a room temperature experiment in which a displacement imprecision 30 dB below that at the SQL and an imprecision-back-action product $<75\cdot\hbar$ is achieved.

physics.optics↗

arXiv2016

A strongly-coupled $Λ$-type micromechanical system

We study a classical $Λ$-type three-level system based on three high-$Q$ micromechanical beam resonators embedded in a gradient electric field. By modulating the strength of the field at the difference frequency between adjacent beam modes, we realize strong dynamic two-mode coupling, via the dielectric force. Driving adjacent pairs simultaneously, we observe the formation of a purely mechanical 'dark' state and an all-phononic analog of coherent population trapping --- signatures of strong three-mode coupling. The $Λ$-type micromechanical system is a natural extention of previously demonstrated 'two-level' micromechanical systems and offers new perspectives on the architecture of all-phononic micromechanical circuits and arrays.

cond-mat.mes-hall↗