No abstract

Conversion between signals in the microwave and optical domains is of great interest both for classical telecommunication, as well as for connecting future superconducting quantum computers into a global quantum network. For quantum applications, the conversion has to be both efficient, as well as operate in a regime of minimal added classical noise. While efficient conversion has been demonstrated with several approaches using mechanical transducers, they have so far all operated with a substantial thermal noise background. Here, we overcome this limitation and demonstrate coherent conversion between GHz microwave signals and the optical telecom band with a thermal background of less than one phonon. We use an electro-opto-mechanical device, that couples surface acoustic waves driven by a resonant microwave signal to an optomechanical crystal featuring a 2.7 GHz mechanical mode. By operating at Millikelvin temperatures, we can initialize the mechanical mode in its quantum groundstate, which allows us to perform the transduction process with less than one quantum of added thermal noise. We further verify the preservation of the coherence of the microwave signal throughout the transduction process. * These authors contributed equally to this work. † s.groeblacher@tudelft.nl arXiv:1812.07588v1 [quant-ph]

Spectrometry is widely used for the characterization of materials, tissues, and gases, and the need for size and cost scaling is driving the development of mini and microspectrometers. While nanophotonic devices provide narrowband filtering that can be used for spectrometry, their practical application has been hampered by the difficulty of integrating tuning and read-out structures. Here, a nano-opto-electro-mechanical system is presented where the three functionalities of transduction, actuation, and detection are integrated, resulting in a high-resolution spectrometer with a micrometer-scale footprint. The system consists of an electromechanically tunable double-membrane photonic crystal cavity with an integrated quantum dot photodiode. Using this structure, we demonstrate a resonance modulation spectroscopy technique that provides subpicometer wavelength resolution. We show its application in the measurement of narrow gas absorption lines and in the interrogation of fiber Bragg gratings. We also explore its operation as displacement-to-photocurrent transducer, demonstrating optomechanical displacement sensing with integrated photocurrent read-out.

The authors report lasing of InAs∕InGaAsP∕InP (100) quantum dots (QDs) wavelength tuned into the 1.55μm telecom region. Wavelength control of the InAs QDs in an InGaAsP∕InP waveguide is based on the suppression of As∕P exchange through ultrathin GaAs interlayers. The narrow ridge-waveguide QD lasers operate in continuous wave mode at room temperature on the QD ground state transition. The low threshold current density of 580A∕cm2 and low transparency current density of 6A∕cm2 per QD layer, measured in pulsed mode, are accompanied by low loss and high gain with an 80-nm-wide gain spectrum.

We demonstrate the control of the spontaneous emission rate of single InAs quantum dots embedded in a double-membrane photonic crystal cavity by the electromechanical tuning of the cavity resonance. Controlling the separation between the two membranes with an electrostatic field we obtain the real-time spectral alignment of the cavity mode to the excitonic line and we observe an enhancement of the spontaneous emission rate at resonance. The cavity has been tuned over 13 nm without shifting the exciton energies. A spontaneous emission enhancement of ≈ 4.5 has been achieved with a coupling efficiency of the dot to the mode β ≈ 92%.The coupling of a quantum emitter such as a quantum dot (QD) to a semiconductor photonic crystal cavity (PCC) has shown to be a promising method to realize single photon sources on a chip, 1 enabling applications in quantum key distribution and quantum photonic integrated circuits (QPIC). Two-dimensional PCCs are commonly used for this purpose due to the high achievable Q factors and small mode volumes. 2,3 The spontaneous emission rate of a two-level system is strongly affected by the local density of optical states provided by the surrounding electromagnetic resonator 4 and can be enhanced or suppressed depending on the spectral alignment between emitter and cavity. The spectral control of QDs has been already achieved using different methods such as temperature tuning, 5,6 Stark effect 7 and strain tuning, 8 while the control of the cavity resonance is more challenging. Cavity tuning has been obtained by controlled gas adsorption and local heating, 9,10 however this technique produces a permanent change in the QD emission energy preventing the separate control of QD and cavity. For QPIC applications, where many devices have to operate at the same wavelength, it is essential to tune each cavity independently over a wide wavelength range (> 10 nm), without affecting the QD emission wavelength and the Q factor. An attractive solution which fulfills all these requirements is provided by nano-opto-electro-mechanical structures (NOEMS). Previous works have demonstrated reconfigurable PCCs based on the electrostatic actuation of laterally coupled nanobeams, 11,12 slotted cavities 13 and twodimensional PCCs on double membranes. 14,15 The use of a vertically-coupled double-membrane is particularly convenient since it allows us to separate the QD layer from the actuation region in the vertical direction, removing any possible interaction between the electrostatic a) l.midolo@tue.nl field and the QDs. When two PCCs are brought at small distances (see inset Figure 1(a)) they couple evanescently, producing a splitting in a symmetric and an antisymmetric mode which shift in wavelength depending on the distance between the membranes. This technique has been demonstrated on InGaAsP/InP, 15 and has been shown not to affect the cavity Q. 14 However the operation at cryogenic temperatures (which is fundamental for QPIC applications) and the tuning to a single quantum dot have not yet been shown. In this ...