Solotronics, optoelectronics based on solitary dopants, is an emerging field of research and technology reaching the ultimate limit of miniaturization. It aims at exploiting quantum properties of individual ions or defects embedded in a semiconductor matrix. It has already been shown that optical control of a magnetic ion spin is feasible using the carriers confined in a quantum dot. However, a serious obstacle was the quenching of the exciton luminescence by magnetic impurities. Here we show, by photoluminescence studies on thus-far-unexplored individual CdTe dots with a single cobalt ion and CdSe dots with a single manganese ion, that even if energetically allowed, nonradiative exciton recombination through single-magnetic-ion intra-ionic transitions is negligible in such zero-dimensional structures. This opens solotronics for a wide range of as yet unconsidered systems. On the basis of results of our single-spin relaxation experiments and on the material trends, we identify optimal magnetic-ion quantum dot systems for implementation of a single-ion-based spin memory.
We propose a novel type of composite light-matter interferometer based on a supersolid-like phase of a driven Bose-Einstein condensate coupled to a pair of degenerate counterpropagating electromagnetic modes of an optical ring cavity. The supersolid-like condensate under the influence of the gravity drags the cavity optical potential with itself, thereby changing the relative phase of the two cavity electromagnetic fields. Monitoring the phase evolution of the cavity output fields thus allows for a nondestructive measurement of the gravitational acceleration. We show that the sensitivity of the proposed gravimeter exhibits Heisenberg-like scaling with respect to the atom number. As the relative phase of the cavity fields is insensitive to photon losses, the gravimeter is robust against these deleterious effects. For state-of-the-art experimental parameters, the relative sensitivity ∆g/g of such a gravimeter could be of the order of 10 −10 -10 −8 for a condensate of a half a million atoms and interrogation time of the order of a few seconds.Introduction.-Precision measurement plays a vital role in fundamental sciences as well as technological applications. Notably, at the beginning of the twentieth century discrepancies between precise measurements and theory led to the birth of quantum mechanics [1]. Interestingly, quantum mechanics itself in turn opened an entirely new avenue in precision measurement. One of its most flourishing branches is quantum metrology, which exploits the quantum-mechanical framework to perform even more precise measurements than it is allowed by classical approaches [2,3]. Remarkable examples include the development of precise "gravimeters" based on quantum mechanical effects.A gravimeter is an apparatus that measures the local gravitational acceleration. It allows to measure, e.g., magma build-up before volcanic eruptions, hidden hydrocarbon reserves, and Earth's tides [4]. In addition, it also allows to test more fundamental aspects of physics such as local Lorentz invariance [5], the isotropy of post-Newtonian gravity [6], and quantum gravity [7]. The current generation of gravimeters include: microelectromechanical gravimeters [4], free-fall gravimeters [8][9][10][11][12], spring-based gravimeters [13,14], superconducting gravimeters [15], optomechanical gravimeters [16,17], and atom interferometers [18][19][20][21][22][23].In the above list, the atom interferometry deserves a special position because of the possibility of harnessing quantum features of many-body systems [24]. In principle, by using entangled resources, it is possible to increase the precision of measurement over the shot-noise limit [25]. However, noise and decoherence limit the creation and use of quantum correlations [26,27], especially for large samples. Hence, sub-shot-noise interferometry is currently restricted to proof-of-principle experiments with atoms [28][29][30][31][32][33][34] as well as photons [35][36][37][38][39].In this Letter, we propose a novel type of gravimeter based on a supersolid-like state of...
We show that the quantum Fisher information attained in an adiabatic approach to critical quantum metrology cannot lead to the Heisenberg limit of precision and therefore regular quantum metrology under optimal settings is always superior. Furthermore, we argue that even though shortcuts to adiabaticity can arbitrarily decrease the time of preparing critical ground states, they cannot be used to achieve or overcome the Heisenberg limit for quantum parameter estimation in adiabatic critical quantum metrology. As case studies, we explore the application of counter-diabatic driving to the Landau-Zener model and the quantum Rabi model.
The characterization of entanglement is a central problem for the study of quantum many-body dynamics. Here, we propose the quantum Fisher information as a useful tool for the study of multipartite-entanglement dynamics in many-body systems. We illustrate this by considering the regular-to-ergodic transition in the Dicke model-a fully-connected spin model showing quantum thermalization above a critical interaction strength. We show that the QFI has a rich dynamical behavior which drastically changes across the transition. In particular, the asymptotic value of the QFI, as well as its characteristic timescales, witness the transition both through their dependence on the interaction strength and through the scaling with the system size. Since the QFI also sets the ultimate bound for the precision of parameter estimation, it provides a metrological perspective on the characterization of entanglement dynamics in many-body systems. Here we show that quantum ergodic dynamics allows for a much faster production of metrologically useful states.
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