28 research outputs found
Amplitude- and phase-resolved nano-spectral imaging of phonon polaritons in hexagonal boron nitride
Phonon polaritons are quasiparticles resulting from strong coupling of
photons with optical phonons. Excitation and control of these quasiparticles in
2D materials offer the opportunity to confine and transport light at the
nanoscale. Here, we image the phonon polariton (PhP) spectral response in thin
hexagonal boron nitride (hBN) crystals as a representative 2D material using
amplitude- and phase-resolved near-field interferometry with broadband mid-IR
synchrotron radiation. The large spectral bandwidth enables the simultaneous
measurement of both out-of-plane (780 cm-1) and in-plane (1370 cm-1) hBN phonon
modes. In contrast to the strong and dispersive in-plane mode, the out-of-plane
mode PhP response is weak. Measurements of the PhP wavelength reveal a
proportional dependence on sample thickness for thin hBN flakes, which can be
understood by a general model describing two-dimensional polariton excitation
in ultrathin materials
Phase-Resolved Rydberg Atom Field Sensing using Quantum Interferometry
Although Rydberg atom-based electric field sensing provides key advantages
over traditional antenna-based detection, it remains limited by the need for a
local oscillator (LO) for low-field and phase resolved detection. In this work,
we demonstrate that closed-loop quantum interferometric schemes can be used to
generate a system-internal reference that can directly replace an external LO
for Rydberg field sensing. We reveal that this quantum-interferometrically
defined internal reference phase and frequency can be used analogously to a
traditional LO for atom-based down-mixing to an intermediate frequency for
lock-in phase detection. We demonstrate that this LO-equivalent functionality
provides analogous benefits to an LO, including full 360 phase
resolution as well as improved sensitivity. The general applicability of this
approach is confirmed by demodulating a four phase-state signal broadcast on
the atoms. Our approach opens up new sensing schemes and provides a clear path
towards all-optical Rydberg atom sensing implementations
Sensitivity Comparison of Two-photon vs Three-photon Rydberg Electrometry
We investigate the sensitivity of three-photon EIT in Rydberg atoms to radio
frequency detection and compare it against conventional two-photon systems.
Specifically, we model the 4-level and 5-level atomic system and compare how
the transmission of the probe changes with different powers of the lasers used
and strengths of the RF field. In this model, we also define a sensitivity
metric to best relate to the operation of the current best experimental
implementation based on shot noise limited detection. We find that the
three-photon system boasts much narrower line widths compared to the
conventional two-photon EIT. However, these narrow line features do not align
with the regions of the best sensitivity. In addition to this, we calculate the
expected sensitivity for the two-photon Rydberg sensor and find that the best
achievable sensitivity is over an order of magnitude better than the current
measured values of 5 uV/m/Hz. However, by accounting for the additional noise
sources in the experiment and the quantum efficiency of the photo-detectors,
the values are in good agreement.Comment: 9 pages, 6 figure
Detection of HF and VHF Fields through Floquet Sideband Gaps by `Rabi Matching' Dressed Rydberg Atoms
Radio frequencies in the HF and VHF (3 MHz to 300 MHz) bands are challenging
for Rydberg atom-based detection schemes, as resonant detection requires
exciting the atoms to extremely high energy states. We demonstrate a method for
detecting and measuring radio frequency (RF) carriers in the HF and VHF bands
via a controlled Autler-Townes line splitting. Using a resonant, high-frequency
(GHz) RF field, the absorption signal from Townes-Merrit sidebands created by a
low frequency, non-resonant RF field can be enhanced. Notably, this technique
uses a measurement of the optical frequency separation of an avoided crossing
to determine the amplitude of a non-resonant, low frequency RF field. This
technique also provides frequency-selective measurements of low frequency RF
electric fields. To show this, we demonstrate amplitude modulated signal
transduction on a low frequency VHF carrier. We further demonstrate reception
of multiple tones simultaneously, creating a Rydberg `spectrum analyzer' over
the VHF range.Comment: Data for figures can be found at:
https://datapub.nist.gov/od/id/mds2-285
Microwave Near-Field Imaging of Two-Dimensional Semiconductors
Optimizing new generations of two-dimensional devices based on van der Waals materials will require techniques capable of measuring variations in electronic properties in situ and with nanometer spatial resolution. We perform scanning microwave microscopy (SMM) imaging of single layers of MoS_2 and n- and p-doped WSe_2. By controlling the sample charge carrier concentration through the applied tip bias, we are able to reversibly control and optimize the SMM contrast to image variations in electronic structure and the localized effects of surface contaminants. By further performing tip bias-dependent point spectroscopy together with finite element simulations, we distinguish the effects of the quantum capacitance and determine the local dominant charge carrier species and dopant concentration. These results underscore the capability of SMM for the study of 2D materials to image, identify, and study electronic defects
Microwave Near-Field Imaging of Two-Dimensional Semiconductors
Optimizing new generations of two-dimensional devices based on van der Waals materials will require techniques capable of measuring variations in electronic properties in situ and with nanometer spatial resolution. We perform scanning microwave microscopy (SMM) imaging of single layers of MoS_2 and n- and p-doped WSe_2. By controlling the sample charge carrier concentration through the applied tip bias, we are able to reversibly control and optimize the SMM contrast to image variations in electronic structure and the localized effects of surface contaminants. By further performing tip bias-dependent point spectroscopy together with finite element simulations, we distinguish the effects of the quantum capacitance and determine the local dominant charge carrier species and dopant concentration. These results underscore the capability of SMM for the study of 2D materials to image, identify, and study electronic defects