Chenglong You

Optimized aperiodic broadband visible absorbers

We present optimized aperiodic structures for use as broadband thermal incandescent emitters which are capable of increasing the emittance by nearly a factor of two over the visible wavelength range when compared to bulk tungsten. These aperiodic multilayer structures are designed with alternating layers of tungsten and air or tungsten and silicon carbide on top of a tungsten substrate. We investigate the properties of these structures for use as lightbulb filaments. We find that these structures greatly enhance the emittance over the visible wavelength range, while also increasing the overall efficiency of the bulb and could lead to a decrease in incandescent lightbulb power consumption by nearly 50%. OCIS codes: (350.4238) Nanophotonics and photonic crystals; (260.0260) Physical optics; (290.6815) Thermal emission.

Multiparameter estimation with single photons—linearly-optically generated quantum entanglement beats the shotnoise limit

It was suggested in Ref. [Phys. Rev. Lett. 114, 170802] that optical networks with relatively inexpensive overhead---single photon Fock states, passive optical elements, and single photon detection---can show significant improvements over classical strategies for single-parameter estimation, when the number of modes in the network is small (n < 7). A similar case was made in Ref. [Phys. Rev. Lett. 111, 070403] for multi-parameter estimation, where measurement is instead made using photon-number resolving detectors. In this paper, we analytically compute the quantum Cramer-Rao bound to show these networks can have a constant-factor quantum advantage in multi-parameter estimation for even large number of modes. Additionally, we provide a simplified measurement scheme using only single-photon (on-off) detectors that is capable of approximately obtaining this sensitivity for a small number of modes.

Nearly optimal measurement schemes in a noisy Mach-Zehnder interferometer with coherent and squeezed vacuum

The use of an interferometer to perform an ultra-precise parameter estimation under noisy conditions is a challenging task. Here we discuss nearly optimal measurement schemes for a well known, sensitive input state, squeezed vacuum and coherent light. We find that a single mode intensity measurement, while the simplest and able to beat the shot-noise limit, is outperformed by other measurement schemes in the low-power regime. However, at high powers, intensity measurement is only outperformed by a small factor. Specifically, we confirm, that an optimal measurement choice under lossless conditions is the parity measurement. In addition, we also discuss the performance of several other common measurement schemes when considering photon loss, detector efficiency, phase drift, and thermal photon noise. We conclude that, with noise considerations, homodyne remains near optimal in both the low and high power regimes. Surprisingly, some of the remaining investigated measurement schemes, including the previous optimal parity measurement, do not remain even near optimal when noise is introduced.

Optimized mid-infrared thermal emitters for applications in aircraft countermeasures

We introduce an optimized aperiodic multilayer structure capable of broad angle and high temperature thermal emission over the 3 μm to 5 μm atmospheric transmission band. This aperiodic multilayer structure composed of alternating layers of silicon carbide and graphite on top of a tungsten substrate exhibits near maximal emittance in a 2 μm wavelength range centered in the mid-wavelength infrared band traditionally utilized for atmospheric transmission. We optimize the layer thicknesses using a hybrid optimization algorithm coupled to a transfer matrix code to maximize the power emitted in this mid-infrared range normal to the structure’s surface. We investigate possible applications for these structures in mimicking 800–1000 K aircraft engine thermal emission signatures and in improving countermeasure effectiveness against hyperspectral imagers. We find these structures capable of matching the Planck blackbody curve in the selected infrared range with relatively sharp cutoffs on either side, leading to i...

Graphene-based dual-band independently tunable infrared absorber

In this paper, we theoretically demonstrate a dual-band independently tunable absorber consisting of a stacked graphene nanodisk and graphene layer with nanohole structure, and a metal reflector spaced by insulator layers. This structure exhibits a dipole resonance mode in graphene nanodisks and a quadrupole resonance mode in the graphene layer with nanoholes, which results in the enhancement of absorption over a wide range of incident angles for both TE and TM polarizations. The peak absorption wavelength is analyzed in detail for different geometrical parameters and the Fermi energy levels of graphene. The results show that both peaks of the absorber can be tuned dynamically and simultaneously by varying the Fermi energy level of graphene nanodisks and graphene layer with nanoholes structure. In addition, one can also independently tune each resonant frequency by only changing the Fermi energy level of one graphene layer. Such a device could be used as a chemical sensor, detector or multi-band absorber.

Fundamental precision limit of a Mach-Zehnder interferometric sensor when one of the inputs is the vacuum

In the lore of quantum metrology, one often hears (or reads) the following no-go theorem: If you put vacuum into one input port of a balanced Mach-Zehnder Interferometer, then no matter what you put into the other input port, and no matter what your detection scheme, the sensitivity can never be better than the shot noise limit (SNL). Often the proof of this theorem is cited to be in Ref. [C. Caves, Phys. Rev. D 23, 1693 (1981)], but upon further inspection, no such claim is made there. A quantum-Fisher-information-based argument suggestive of this no-go theorem appears in Ref. [M. Lang and C. Caves, Phys. Rev. Lett. 111, 173601 (2013)], but is not stated in its full generality. Here we thoroughly explore this no-go theorem and give the rigorous statement: the no-go theorem holds whenever the unknown phase shift is split between both arms of the interferometer, but remarkably does not hold when only one arm has the unknown phase shift. In the latter scenario, we provide an explicit measurement strategy that beats the SNL. We also point out that these two scenarios are physically different and correspond to different types of sensing applications.