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

Zeeman-resolved Autler-Townes splitting in Rydberg atoms with tunable resonances and a single transition dipole moment

Applying a magnetic field as a method for tuning the frequency of Autler-Townes splitting for Rydberg electrometry has recently been demonstrated. In this paper we provide a theoretical understanding of EIT signals in the presence of a large magnetic field, as well as demonstrate some advantages of this technique over traditional Autler-Townes based electrometry. We show that a strong magnetic field provides a well-defined quantization axis regardless of the optical field polarizations, we demonstrate that by separating the $m_J$ levels of the Rydberg state we can perform an Autler-Townes splitting with a single participating dipole moment, and we demonstrate recovery of signal strength by populating a single $m_J$ level using circularly polarized light

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$^\circ$ 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

Independent Rydberg Atom Sensing using a Dual-Ladder Scheme

Rydberg atom-based electric field sensing can provide all-optical readout of radio frequency fields in a dielectric environment. However, because a single set of optical fields is typically used to prepare the Rydberg state and read out its response to RF fields, it is challenging to perform simultaneous and independent measurements of the RF field(s). Here we show that using two independent schemes to prepare and read out the same Rydberg state can be used to perform independent measurements in general, which we demonstrate specifically by resolving the the RF polarization. We expect this work will be useful for fiber-coupled sensor heads where spatial multiplexing is challenging, as well as for complex multi-level sensing schemes

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