One of the advantages of Rydberg atom-based detection of microwave and THz fields is weak distortion of the measured field, allowing for precise and stealthy detection. However, recent developments focused on using Rydberg atoms as a RF mixer with a local oscillator field in a superheterodyne-type detection that is no longer all-optical, as the local oscillator antenna has to be a part of the detector. Here we undertake the task of developing an all-optical detection, where the phase reference is provided not in local oscillator, but instead in the polarization of atoms. To realize this feature, we access the 13.9 GHz Rydberg transition in rubidium with two separate optical excitation paths and measure the beating of probe field. We report an overall detection sensitivity of 176 nV/cm/ √Hz and reliable operation up to 3.5 mV/cm of RF field, results that are parallel to superheterodyne detection method demonstrated in the same setup. The results of this work are largely based on an earlier conducted study, published as a preprint.1 The present manuscript is meant to serve as an appendix to this work, focusing on putting this research in the context of all-optical detection schemes.
One of the advantages of Rydberg atom-based detection of microwave and THz fields is weak distortion of the measured field, allowing for precise and stealthy detection. However, recent developments focused on using Rydberg atoms as a RF mixer with a local oscillator field in a superheterodyne-type detection that is no longer all-optical, as the local oscillator antenna has to be a part of the detector. Here we undertake the task of developing an all-optical detection, where the phase reference is provided not in local oscillator, but instead in the polarization of atoms. To realize this feature, we access the 13.9 GHz Rydberg transition in rubidium with two separate optical excitation paths and measure the beating of probe field. We report an overall detection sensitivity of 176 nV/cm/ √Hz and reliable operation up to 3.5 mV/cm of RF field, results that are parallel to superheterodyne detection method demonstrated in the same setup. The results of this work are largely based on an earlier conducted study, published as a preprint.1 The present manuscript is meant to serve as an appendix to this work, focusing on putting this research in the context of all-optical detection schemes.
The detection of microwave (MW) fields with room-temperature Rydberg atomic vapors is a novel technique of optical sensing, introducing a range of merits typically not possible to achieve with conventional antennas [1]. Firstly, the atomic response to MW fields is dependent on a given transition dipole moment between Rydberg energy levels - as this value can be precisely derived from the theory of alkali atoms, e.g. rubidium, Rydberg sensors are intrinsically calibrated and there is no dependency on particular device. Secondly, the detector does not contain any metal parts (apart from trace amount of rubidium), introducing very little distortion to the measured field, so the detection is stealthy, and the detector is practically invulnerable even to strong fields. Typically, however, the best state-of-the-art performance is achieved with an additional local oscillator MW field [2], emitted from the antenna, in which case the scheme is no longer all-optical and some advantages are lost.
Abstract Coupling a Rydberg vapour medium to both microwave and optical fields enables the benefits of all-optical detection, such as minimal disturbance of the measured field and resilience to very strong signals, since no conventional antenna is required. However, peak sensitivity typically relies on adding a microwave local oscillator, which compromises the all-optical nature of the measurement. Here we introduce an alternative, optical-bias detection , that maintains fully optical operation while achieving high sensitivity. To address laser phase noise, which is critical in this approach, we perform a simultaneous measurement of the noise using a nonlinear process and correct it in real time via data processing. This yields a 35 dB improvement in signal-to-noise ratio compared with the basic method. We demonstrate a sensitivity of 176nV/cm/Hz 176 nV / cm / Hz , reliable operation up to 3.5 mV/cm at 13.9 GHz, and quadrature-amplitude modulated data transmission, underlining the ability to detect microwave field quadratures while preserving the unique advantages of all-optical detection.
Recently, a Rydberg atom-based mixer was developed to measure the phase of a radio frequency (RF) field. The phase of the signal RF (SIG RF) field is down-converted directly to the phase of a beat signal created by the presence of a local RF (LO RF) field. In this study, we propose that the Rydberg atom-based mixer can be converted to an all-optical phase detector by amplitude modulation (AM) of the LO RF field; that is, the phase of the SIG RF field is related to both the amplitude and phase of the beat signal. When the AM frequency of the LO RF field is the same as the frequency of the beat signal, the beat signal will further interfere with the AM of the LO RF field inside the atom, and then the amplitude of the beat signal is related to the phase of the SIG RF field. The amplitude of the beat signal and the phase of the SIG RF field show a linear relationship within the range of 0 to π/2 when the phase of the AM is set with a difference π/4 from the phase of the LO RF field. The minimum phase resolution can be as small as 0.6° by optimizing the experimental conditions according to a simple theoretical model. This study will expand and contribute to the development of RF measurement devices based on Rydberg atoms.
Significant progress has been made in atom-based measurements of length, time, gravity and electromagnetic fields in recently years. Rydberg atom-based microwave electric field measurement, using electromagnetically induced transparency (EIT) in room temperature alkali-metal vapors, has been extensively investigated and aroused the broad interest. This approach may establish a new standard for the measurements of microwave (MW) and radio frequency (RF) electric fields.In this review, we describe the work on a new method of measuring electric fields based on quantum interference by using either cesium or rubidium atoms contained in a dielectric vapor cell. Rydberg atoms with principal quantum number n >>1 have large direct current (DC) polarizabilities and microwave transition dipole moments, thereby making them extremely sensitive to external electric fields. Using the Rydberg three-level EIT to detect the level splitting and shift that is induced by the external field, we can realize a rapid and robust self-calibration method of measuring the electric field in a frequency range from 0.01 GHz to 1000 GHz. For the MW electric field (frequency range > 1 GHz), the MW field causes the Rydberg states to split, known as an Autler-Townes splitting (A-T) effect when the applied microwave can resonate with adjacent Rydberg states. The MW coupled A-T splitting is proportional to the applied electric field strength, from which the field strength is measured. Using the EIT window, a high sensitivity of 3 μV·cm-1·Hz-1/2 and small electric field of 1 μV/cm are expected to be achieved with a modest setup, and the limitations of the sensitivity are also addressed in the review. For the RF field at frequency mj EIT lines, and avoided crossings formed with the fine-structure levels of equal mj and different J's, which is used to calibrate and measure the RF field amplitude. On the other hand, the dependence of the EIT-line strength on the RF field polarization provides a fast and robust polarization measurement of RF fields based on matching experimental data with a theoretical simulation. The measurements of minimum strengths and sensitivity of RF fields based on Rydberg atoms are one order magnitude below the values obtained by traditional antenna methods. The atom-based field measurement paves the way for determining fields through calibration-free, invariable atomic properties and miniaturization. We also propose its various potential applications in the future.
Rydberg atom radio-frequency sensors are a unique platform for precision electromagnetic field measurement; e.g., they have extraordinary carrier bandwidth spanning MHz to THz and can be self-calibrated. These photonic sensors use lasers to prepare and read out the atomic response to a radio-frequency electromagnetic field. Most work on Rydberg atom sensors centers on radio-frequency electric field strength because the sensor functions as a square law detector, unless an external radio-frequency heterodyning field is used. A heterodyning field acts as a local oscillator and enables phase readout at the expense of the radio-frequency equipment necessary to generate it. In order to overcome the disadvantages of a radio-frequency local oscillator, we investigate all-optical phase-sensitive detection using a five-level closed-loop excitation scheme. We show that under finite detuning of the loop fields, the atomic response oscillates at the frequency of the detuning. The oscillation is transferred to a probe laser absorption signal. The phase, frequency, and amplitude of the radio-frequency signal are imprinted on the oscillatory dynamics and can be determined using demodulation and matched filter techniques applied to the probe laser transmission signal.
An antenna is a key component of E-field signal pickup. However, an antenna has major limitations due to the metal-based probes, the geometry it carries, and the use of metal transmission lines; this can lead to perturbations or disturbance of the fields which limits the precision for field sensing. Rydberg atoms such as Cesium (Cs) or Rubidium (Rb) are utilized for Rydberg sensing. This can be utilized over a large range of frequencies from DC MHz and THz upto (>100 GHz) to measure amplitude, polarization, power, phase, and Angle-of-Arrival of RF Efield. Rydberg sensor detection scheme provides a multitude of applications, including far field characterization using near field or subwavelength imaging, strong RF E-field measurements, weak field detections, mapping of microwave circuitry, Binary Phase Shift Keying (BPSK), Quadrature Amplitude Modulation (QAM) and Quadrature Phase Shift Keying (QPSK) signals, metrology, and radars. Recently, practical RF E-field probes such as the RFP and movable probe have been prototyped for application specific RF sensing and measurement needs, further, antenna and waveguide embedded Rydberg sensors have also been developed. Few limitations in the Rydberg sensing scheme are due to lasers, EIT line-width, earth magnetic effects, photodiode circuit noise, and vapor cell in-homogeneity. The purpose of the review is to brief about the thematic work done across the Rydberg atom domain and its applications as RF E-field sensors. The findings of this review indicate the advantages and applications of Rydberg atom sensing as well as the gaps and uncertainties the scheme carries.