Ultrasensitive micro-scale parity-time-symmetric ring laser gyroscope

Abstract

We propose a new scheme for ultrasensitive laser gyroscopes that utilizes the physics of exceptional points. By exploiting the properties of such non-Hermitian degeneracies, we show that the rotation-induced frequency splitting becomes proportional to the square root of the gyration speed (√ )-thus enhancing the sensitivity to low angular rotations by orders of magnitudes. In addition, at its maximum sensitivity limit, the measurable spectral splitting is independent of the radius of the rings involved. Our work paves the way towards a new class of ultrasensitive miniature ring laser gyroscopes on chip. © 2017 Optical Society of America In 1913, Sagnac demonstrated how the rate of rotation associated with an inertial frame of reference can be determined by optical means. In his experiments, the rotation speed was measured through the phase difference between two beams traveling in opposite directions within a loop. Since then, this approach has been successfully used to develop various families of optical rotational sensors [1,2]. A breakthrough in this area came shortly after the discovery of the laser, when Macek and Davis introduced gain in the ring cavity [3]. In this respect, the phase shift between the two counter-propagating beams is effectively converted into a splitting in the resonant frequencies that can in turn be readily measured.In an ideal non-rotating ring laser, the two counterpropagating modes are expected to exhibit the same frequency. On the other hand, if this same system rotates at an angular frequency , the two initially degenerate resonant frequencies split, according to the following expression Δ = 8 Ω.(1) Here and are the enclosed area and the perimeter of the ring, respectively, and is the wavelength within the material associated with this cavity. Ideally, as long as the frequency separation (Δ ) exceeds the quantum limit imposed by the spontaneous emission noise, the rotation speed Ω can be uniquely determined through a heterodyne measurement. For example, for a ring laser with a radius of 10 cm, operating at a wavelength of 1.55 μm, and rotating at a rate of ~10°/hour, one can expect a frequency splitting that is at best on the order of ~ 12 Hz [1]. In many consumer and industrial applications, it is required to detect angular velocities in the range of ~0.1 − 100°/hour -a precision that can be readily attained in state-of-the-art free-space ring laser gyroscopes [4]. Unfortunately however, such sensitivity levels have so far remained practically out-of-reach in fully integrated optical platforms, where the area of the loop is generally smaller, perhaps by several orders of magnitudes. In addition, in on-chip settings, light scattering from the cavity walls can prove detrimental. This is because the ensuing unwanted coupling between the two counter-propagating modes can lead to a lock-in effect, rendering this method ineffective below a certain rotation speed.Currently, several efforts are underway to implement chip-scale laser gyroscopes based on different strategies. One possible ...

Quantum exceptional points of non-Hermitian Hamiltonians and Liouvillians: The effects of quantum jumps

“…The advantages of EPs for applications remain a very active topic of research [16,[59][60][61][62][63][64][65][66][67][68][69][70][71][72] and correctly modelling noise and quantum jumps is fundamental to correctly adress the question of, e.g., EPs sensitivity. We believe that our work, showing explicitly the operational interpretation and the relation between classical and quantum EPs in terms of postselection and/or inefficient detectors, can stimulate more interest in experimental demonstrations of LEPs and their potential quantum applications, pointing out analogies and differences with respect to those studied for semiclassical HEPs.…”

Large Sagnac frequency splitting in a ring resonator operating at an exceptional point

“…One of ring resonators satisfying condition (3) is a coupled ring resonator with parity-time symmetry [31]. However, the resonator structure leads to rotation dependence of the eigenmode loss (or amplification), which may affect the sensitivity of rotation detection.…”

“…Meanwhile, a general theory on the sensitivity enhancement of sensors using resonators has been recently presented in the context of non-Hermitian physics in microcavities [27], and several applications have been proposed [28][29][30][31]. The basic idea of the enhancement is to use an anomalous perturbation response at the so-called exceptional point (EP) in nonHermitian resonator systems.…”

Quantum Sensing with a Single-Qubit Pseudo-Hermitian System

“…The discovery has opened a new avenue to intriguing non-Hermitian physics in both classical and quantum systems [10][11][12][13][14][15][16][17][18][19][20][21][22][23][24]. In particular, the concepts of exceptional point [25][26][27] and PT -phase transition [28,29] lead to important experimental observations such as single-mode lasers [30, 31], non-reciprocal light transport [32, 33], non-Hermitian topological light steering [34], asymmetric mode switching [35] and topological energy transfer [36] when encircling an exceptional point.Among a number of important applications, enhancing the sensitivity of energy splitting detection by using exceptional points attracts increasingly intensive theoretical interest [37][38][39][40][41][42]. The unique feature of exceptional point based sensing is the divergent eigenvalue susceptibility arising from the square-root frequency topology around exceptional points [27].…”

“…Among a number of important applications, enhancing the sensitivity of energy splitting detection by using exceptional points attracts increasingly intensive theoretical interest [37][38][39][40][41][42]. The unique feature of exceptional point based sensing is the divergent eigenvalue susceptibility arising from the square-root frequency topology around exceptional points [27].…”