28 research outputs found
An isotropic antenna based on Rydberg atoms
Governed by the hairy ball theorem, classical antennas with isotropic
responses to linearly polarized radio waves are unrealizable. This work shows
that the antenna based on Rydberg atoms can theoretically achieve an ideal
isotropic response to linearly polarized radio waves; that is, it has zero
isotropic deviation. Experimental results of isotropic deviation within 5 dB,
and 0.3 dB achievable after optimization, in microwave and terahertz wave
measurements support the theory and are at least 15 dB improvement than the
classical omnidirectional antenna. Combined with the SI traceable and
ultrawideband property, the ideal isotropic response will make radio wave
measurement based on atomic antenna much more accurate and reliable than the
traditional method. This isotropic atomic antenna is an excellent example of
what a tailored quantum sensor can realize, but a classical sensor cannot. It
has crucial applications in fields such as radio wave electrometry
High bandwidth laser-frequency-locking for wideband noise suppression
Ultra-low frequency noise lasers have been widely used in laser-based
experiments. Most narrow-linewidth lasers are implemented by actively
suppressing their frequency noise through a frequency noise servo loop (FNSL).
The loop bandwidths (LBW) of FNSLs are currently below megahertz, which is
gradually tricky to meet application requirements, especially for wideband
quantum sensing experiments. This article has experimentally implemented an
FNSL with loop-delay-limited 3.5 MHz LBW, which is an order higher than the
usual FNSLs. Using this FNSL, we achieved 70 dB laser frequency noise
suppression over 100 kHz Fourier frequency range. This technology has broad
applications in vast fields where wideband laser frequency noise suppression is
inevitable
Noise analysis of the atomic superheterodyne receiver based on flat-top laser beams
Since its theoretical sensitivity is limited by quantum noise, radio wave
sensing based on Rydberg atoms has the potential to replace its traditional
counterparts with higher sensitivity and has developed rapidly in recent years.
However, as the most sensitive atomic radio wave sensor, the atomic
superheterodyne receiver lacks a detailed noise analysis to pave its way to
achieve theoretical sensitivity. In this work, we quantitatively study the
noise power spectrum of the atomic receiver versus the number of atoms, where
the number of atoms is precisely controlled by changing the diameters of
flat-top excitation laser beams. The results show that under the experimental
conditions that the diameters of excitation beams are less than or equal to 2
mm and the read-out frequency is larger than 70 kHz, the sensitivity of the
atomic receiver is limited only by the quantum noise and, in the other
conditions, limited by classical noises. However, the experimental
quantum-projection-noise-limited sensitivity this atomic receiver reaches is
far from the theoretical sensitivity. This is because all atoms involved in
light-atom interaction will contribute to noise, but only a fraction of them
participating in the radio wave transition can provide valuable signals. At the
same time, the calculation of the theoretical sensitivity considers both the
noise and signal are contributed by the same amount of atoms. This work is
essential in making the sensitivity of the atomic receiver reach its ultimate
limit and is significant in quantum precision measurement
Quantum scaling atomic superheterodyne receiver
Measurement sensitivity is one of the critical indicators for Rydberg atomic
radio receivers. This work quantitatively studies the relationship between the
atomic superheterodyne receiver's sensitivity and the number of atoms involved
in the measurement. The atom number is changed by adjusting the length of the
interaction area. The results show that for the ideal case, the sensitivity of
the atomic superheterodyne receiver exhibits a quantum scaling: the amplitude
of its output signal is proportional to the atom number, and the amplitude of
its read-out noise is proportional to the square root of the atom number.
Hence, its sensitivity is inversely proportional to the square root of the atom
number. This work also gives a detailed discussion of the properties of transit
noise in atomic receivers and the influence of some non-ideal factors on
sensitivity scaling. This work is significant in the field of atom-based
quantum precision measurements