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Register a new userResponse to Room Temperature, Quantum-Limited THz Heterodyne Detection? Not Yet
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This commentary is written in response to arXiv:1907.13198. In this article, Zmuidzinas et al. raise questions about the results reported by our group in Nature Astronomy (DOI: 10.1038/s41550-019-0828-6) regarding our experimental methodology and our device performance metrics. As described in this Response, Zmuidzinas et al. have unfortunately missed some basic principles on impedance matching and the physics of photomixers and plasmonics that are at the heart of their categorical conclusions. Here, we correct these misunderstandings and discharge all of their flawed conclusions. Therefore, all of the results and conclusions reported in our Nature Astronomy manuscript remain correct, as before.
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In their article, Wang et al. [1] report a new scheme for THz heterodyne detection using a laser-driven LTG-GaAs photomixer [2, 3] and make the impressive claim of achieving near quantum-limited sensitivity at room temperature. Unfortunately, their experimental methodology is incorrect, and furthermore the paper provides no information on the mixer conversion loss, an important quantity that could readily have been measured and reported as a consistency check. The paper thus offers no reliable experimental evidence that substantiates the claimed sensitivities. To the contrary, the very high value reported for their photomixer impedance strongly suggests that the conversion loss is quite poor and that the actual sensitivity is far worse than claimed.
We demonstrate a high temperature performance quantum detector of Terahertz (THz) radiation based on three-dimensional metamaterial. The metamaterial unit cell consists of an inductor-capacitor (LC) resonator laterally coupled with antenna elements. The absorbing region, consisting of semiconductor quantum wells is contained in the strongly ultra-subwavelength capacitors of the LC structure. The high radiation loss of the antenna allows strongly increased collection efficiency for the incident THz radiation, while the small effective volume of the LC resonator allows intense light-matter coupling with reduced electrical area. As a result, our detectors operates at much higher temperatures than conventional quantum well detectors demonstrated so far.
Fast, room temperature imaging at THz and sub-THz frequencies is an interesting feature which could unleash the full potential of plenty applications in security, healthcare and industrial production. In this Letter we introduce micromechanical bolometers based on silicon nitride trampoline membranes as broad-range detectors, down to the sub-THz frequencies. They show, at the largest wavelengths, room-temperature noise-equivalent-powers comparable to state-of-the-art commercial devices (~100 pW Hz-1/2); adding the good operation speed and the easy, large-scale fabrication process, the trampoline membrane could be the next candidate for cheap, room temperature THz imaging and related applications.
We report on a heterodyne receiver designed to observe the astrophysically important neutral atomic oxygen [OI] line at 4.7448 THz. The local oscillator is a third-order distributed feedback Quantum Cascade Laser operating in continuous wave mode at 4.741 THz. A quasi-optical, superconducting NbN hot electron bolometer is used as the mixer. We recorded a double sideband receiver noise temperature (T^DSB_rec) of 815 K, which is ~7 times the quantum noise limit (h{ u}/2k_B) and an Allan variance time of 15 s at an effective noise fluctuation bandwidth of 18 MHz. Heterodyne performance was confirmed by measuring a methanol line spectrum.
Label-free biosensors are important tools for clinical diagnostics and for studying biology at the single molecule level. The development of optical label-free sensors has allowed extreme sensitivity, but can expose the biological sample to photodamage. Moreover, the fragility and complexity of these sensors can be prohibitive to applications. To overcome these problems, we develop a quantum noise limited exposed-core fiber sensor providing robust platform for label-free biosensing with a natural path toward microfluidic integration. We demonstrate the detection of single nanoparticles down to 25 nm in radius with optical intensities beneath known biophysical damage thresholds.
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