G. S. Agarwal, Tarak Nath Dey, Sunish Menon
We show how the application of a coupling field connecting the two lower metastable states of a lambda-system can produce a variety of new results on the propagation of a weak electromagnetic pulse. In principle the light propagation can be changed from subluminal to superluminal. The negative group index results from the regions of anomalous dispersion and gain in susceptibility.
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In this paper, we investigate tunable control of the group velocity of a weak probe field propagating through an f-deformed Bose-Einstein condensate of three-level atoms beyond the rotating wave approximation. For this purpose, we use an f- deformed generalization of an effective two-level quantum model of the three-level configuration without the rotating wave approximation in which the Gardiners phonon operators for Bose-Einstein condensate are deformed by an operator- valued function,f(n), of the particle- number operator n . Corrections produced by the counter- rotating terms appear in the…
In this paper, we investigate the propagation of a weak optical probe pulse in an f-deformed Bose- Einstein condensate (BEC) of a gas with the -type three- level atoms in the electromagnetically induced transparency (EIT) regime. We use an f- deformed generalization of an effective two- level quantum model of the three- level configuration in which the Gardiner phonon operators for BEC are deformed by an operator- valued function, f(n), of the particle- number operator n. With making use of the quantum approach of the angular momentum theory we obtain the eigenvalues and eigenfunctions of the …
Subluminal and superluminal velocities of free-space photons
研究自由空间电磁波包的直线传播，发现局域化波包具有亚光速群速和超光速相速，其乘积等于光速平方，揭示了光子波函数的量子描述细节。
We exploit the analogy between tunnelling across a potential barrier and Aharonov's weak measurements to resolve the long standing paradox between the impossibility to exceed the speed of light and the seemingly 'superluminal' behaviur of the tunnelling particle in the barrier. We demonstrate that 'superluminality' occurs when the value of the duration $τ$ spent in the barrier is uncertain, whereas when $τ$ is known accurately, no 'superluminal' behaviur is observed. In all cases only subluminal durations contribute to the transmission, which precludes faster-than-light information transfer, a…
Tunable superluminal reflection and transmission through a slab doped with Raman driven atoms
本文研究电磁脉冲通过掺杂四能级Raman驱动原子平板的反射与透射，通过调节控制场强度可实现脉冲在亚光速与超光速之间的可调切换。
Dispersion and absorption properties of a weak probe field in a three-level V-type atomic system is studied. By application of indirect incoherent pump fields the effect of populating upper levels on optical properties of the atomic medium in presence of a strong coherent pump field is investigated. It is shown that the slope of dispersion changes from positive to negative just by changing the intensity of the coherent or indirect incoherent pump fields. It is demonstrated that the absorption-free subluminal and superluminal light propagation appears in this system.
We examine the propagation of a weak probe light through a coherently driven $Y$-type system. Under the condition that the excited atomic levels decay via same vacuum modes, the effects of quantum interference in decay channels are considered. It is found that the interference in decay channels results in a lossless anomalous dispersion between two gain peaks. We demonstrate that the probe pulse propagation can in principle be switched from subluminal to superluminal due to the decay-induced interference. We also show that the system exhibits a high index of refraction with negligible absorpti…
Comment on 'Quantum principle of relativity'
本文评论 Dragan 和 Ekert 提出的量子相对性原理，指出其超光速与亚光速分支在数学上无法统一，因而该原理不完备。
We consider an optomechanical double-ended cavity under the action of a coupling laser and a probe laser in electromagnetically induced transparency configuration. It is shown how the group delay and advance of the probe field can be controlled by the power of the coupling field. In contrast to single-ended cavities, only allowing for superluminal propagation, possibility of both superluminal and subluminal propagation regimes are found. The magnitudes of the group delay and the advance are calculated to be 1ms and -2s, respectively, at a very low pumping power of a few microwatts. In addition…
We investigate dispersion and absorption properties of a weak probe field in a four level atomic system through interacting dark resonances. We show that two narrow peaks appears in the optical spectra due to the presence of interacting dark resonances. This two narrow peaks leads to the superluminal light propagation with strong absorption. However, if a weak incoherent pump field is exerted to the probe transition, then the peaks structures can be changed such that two absorption peaks transformed to two gain deeps. We Show that both subluminal and superluminal light propagation occur in thi…
Explanation of Superluminal Phenomena Based on Wave-Particle Duality and Proposed Optical Experiments
基于光子波粒二象性解释超光速现象，指出超光速仅发生在相干长度内且不违反因果律，并提议光学实验验证。
Towards a group structure for superluminal velocity boosts
本文构建了超光速速度变换的几何映射，证明了在(1+1)维时空中亚光速与超光速变换的集合构成一个群，为避免与实验相悖的超光速群结构研究提供了新途径。
We study Chiral Based Electromagnetically Induced Transparency (CBEIT) of a light pulse and its associated subluminal and superluminal behavior through a cold and a hot medium of 4-level \textit{double-Lambda type} atomic system. The dynamical behavior of this chiral based system is temperature dependent. The magnetic field based chirality and dispersion is always opposite as compared with the electric field ones. Contrastingly, the response of the chiral effect along with the incoherence Doppler broadening mechanism enhances the superluminal behavior as compared with its traditional degrading…
We analyze the propagation of a pulse across a vacuum gap separating opposite flat parallel faces of two transparent dielectrics by means of an explicitly causal and retarded propagator constructed directly from the free-space wave equation. Nevertheless, our approach yields apparently superluminal propagation for the case of frustrated total internal reflection (FTIR), that is, a transmitted wave packet appears on the far side of the gap at the same time that the corresponding incident packet crosses the front one. Thus, in this example superluminality is just an illusion, being consistent wi…
We show that optical tachyonic dispersion corresponding to superluminal (faster than-light) group velocities characterizes parametrically amplifying media. The turn-on of parametric amplification in finite media, followed by illumination by spectrally narrow probe wavepackets, can give rise to transient tachyonic wavepackets. In the stable (sub-threshold) operating regime of an optical phase conjugator it is possible to transmit probe pulses with a superluminally advanced peak, whereas conjugate reflection is always subluminal. In the unstable (above-threshold) regime, superluminal response oc…
The coherent superposition of two-atomic levels induced by coherent population trapping is employed in a standard $Λ$ type scheme to form a tripod-like system. A weak probe pulse scanning across the system is shown to experience a crossover from absorption to transparent and then to amplification. Consequently the group velocity of the probe pulse can be controlled to propagate either as a subluminal, a standard, a superluminal or even a negative speed. It is shown that the propagation behavior of the light field is entirely determined and controlled by the initial states of the coherent super…
For a transition $F_e=0\leftrightarrow F_g=1$ driven by a linearly polarized light and probed by a circularly light, quantum coherence effects are investigated. Due to the coherence between the drive Rabi frequency and Zeeman splitting, electromagnetically induced transparency, electromagnetically induced absorption, and the transition from positive to negative dispersion are obtained, as well as the populations coherently oscillating in a wide spectral region. At the zero pump-probe detuning, the subluminal and superluminal light propagation is predicted. Finally, coherent population trapping…
We use a one-dimensional model system to compare the predictions of two different 'yardsticks' to compute the position of a particle from its quantum field theoretical state. Based on the first yardstick (defined by the Newton-Wigner position operator), the spatial density can be arbitrarily narrow and its time-evolution is superluminal for short time intervals. Furthermore, two spatially distant particles might be able to interact with each other outside the light cone, which is manifested by an asymmetric spreading of the spatial density. The second yardstick (defined by the quantum field op…
The interaction of a weak probe laser with an inverted-Y type four-level atomic system driven by two additional coherent fields is investigated theoretically. Under the influence of the coherent coupling fields, the steady-state linear susceptibility of the probe laser shows that the system can have single or double electromagnetically induced transparency windows depending on the amplitude and the detuning of the coupling lasers. The corresponding index of refraction associated with the group velocity of the probe laser can be controlled at both transparency windows by the coupling fields. Th…
Phase-Sensitive Enhanced Absorption, Transmission and Slow Light in a Cross-cavity Magnomechanical System
本文研究交叉腔磁力系统中两个探测场相对相位和强度对磁致透明、吸收透射谱及群延迟的调控，实现亚光速与超光速切换，为微波信号调制和量子传感提供新思路。
From Kinematics to Interference: Operational Requirements for the Quantum Principle of Relativity
本文探讨了量子相对性原理中运动学、操作内容和动力学之间的关系，旨在明确实现该原理的必要条件。
We explain the probe field transmission spectrum under the influence of a strong pump field in a hybrid optomechanical system, composed of an optical cavity, a mechanical resonator, and a two-level atom. We show fast (superluminal) and slow (subluminal) light effects of the transmitted probe field in the hybrid system for suitable parametric regimes. For the experimental accessible domain, we find that the fast light effect obtained for the single optomechanical coupling can further be enhanced with the additional atom-field coupling in the hybrid system. Furthermore, we report the existence o…
We investigate the absorption and transmission properties of a weak probe field under the influence of a strong control field in a hybrid cavity magnomechanical system in the microwave regime. This hybrid system consists of two ferromagnetic material yttrium iron garnet (YIG) spheres strongly coupled to a single cavity mode. In addition to two magnon-induced transparency (MIT) that arise due to strong photon-magnon interactions, we observe a magnomechanically induced transparency (MMIT) due to the presence of nonlinear phonon-magnon interaction. In addition, we discuss the emergence and tunabi…
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