A new method is proposed to reduce the frequency noise of a local oscillator to the level of white phase noise by maintaining (not destroying by projective measurement) the coherence of the ensemble pseudo-spin of atoms over many measurement cycles. This method, which we call 'atomic phase lock (APL)', uses weak measurement to monitor the phase in the Ramsey method and repeat the cycle without initialization of the phase. APL will achieve white phase noise as long as the noise accumulated during dead time and the decoherence are smaller than the measurement noise. A numerical simulation confirmed that with APL, the Allan deviation is averaged down at a maximum rate that is proportional to the inverse of the total measurement time, τ⁻¹. In contrast, current atomic clocks that use projection measurement suppress the noise only to the white frequency noise level, in which case the Allan deviation scales as τ^−1/2. Faraday rotation is one way to achieve weak measurement for APL. The strength of Faraday rotation with ¹⁷¹Yb⁺ ions trapped in a linear rf-trap is evaluated, and the performance of APL is discussed. The main source of decoherence is a spontaneous emission, induced by the probe beam for Faraday rotation measurement. The Faraday rotation measurement can be repeated until the decoherence becomes comparable to the signal-to-noise ratio of the measurement. The number of cycles for a realistic experimental parameter is estimated to be ~100.

We report an experimental determination of the diamagnetic correction to the 9Be+ ground state hyperfine constant A. We measured A = $-${}625008837.371(11) Hz at a magnetic field B of 4.4609 T. Comparison with previous results, obtained at lower values of B (0.68 T and 0.82 T), yields the diamagnetic shift coefficient k = 2.63(18)\ifmmode\times\else\texttimes\fi{}10$-${}11 T$-${}2, where A(B)=A0(1+kB2). The zero-field hyperfine constant A0 is determined to be $-${}625008837.044(12) Hz. The g-factor ratio gI$'${}/gJ is determined to be 2.1347798527(10)\ifmmode\times\else\texttimes\fi{}10$-${}4, which is equal to the value measured at lower B to within experimental error. Upper limits are placed on some other corrections to the Breit-Rabi formula. The measured value of k agrees with theoretical estimates.

A method of estimating the propagation delay between two remote sites using a wireless communication module that is compatible with IEEE 802.15.4g is proposed. In our previous paper, we reported that propagation delay due to water vapor can be estimated using digital terrestrial broadcasting waves, which is a passive method from the user's view point. In this paper, we propose an active method that allows the propagation delay between two remote sites of the user's choice to be monitored, as long as a line of sight exists. A real‐time propagation delay monitoring system with wireless communication modules, (wireless two‐way interferometry [Wi‐Wi] modules,) is developed and tested. The data obtained using Wi‐Wi modules separated by 4.25 km show about 14‐cm variation of propagation delay in 1 day, in good agreement with values obtained by ground‐based meteorological observation. This study shows that this technique enables measurement of the surface propagation delay in the horizontal direction with millimeter precision and high spatial and temporal resolution at a low cost.

The importance of reliable information transfer in wireless networks, especially regarding communication delay, is drastically increasing to fulfill safe and high-quality communication in the 5G and post-5G era. However, conventional media access control (MAC) protocol for wireless networks, notably Carrier Sense Multiple Access with Collision Avoidance (CSMA/CA), sometimes yields unexpectedly significant delay due to its complex arbitration mechanism assuming asynchronous communication among terminals. As the delay cannot be strictly bounded by a deterministic value, this causes a vulnerability of systems relying on wireless networks. This paper utilizes precise time synchronization achieved by Wireless Two-way Interferometry (Wi-Wi), enabling all terminals to be time-synchronized via wireless signals. We show that by an appropriate periodic assignment of each terminal's data transmission timing, named Arbitration Point (AP), a simple arbitration algorithm obtains a strictly bounded maximum value for the delay while ensuring equalities among all participants. Furthermore, we demonstrate that the total number of terminals manageable in a star-topology wireless network significantly increases by densely packing AP timings, taking into account the spatial geometry information of terminals, which is another feature delivered by Wi-Wi measurement. In the meantime, we experimentally constructed a star-topology wired network where all terminals are time-synchronized via Wi-Wi to confirm the fundamental properties identified in the proposed arbitration protocol. This study paves a new way for future wireless networks where the delay is strictly bounded and provides the basis for ultra-reliable and high-quality information transfer functionalities by utilizing precise time synchronization and space localization (space-time synchronization).