We study the competing effects of stimulated and spontaneous emission on the information capacity of an amplifying disordered waveguide. At the laser threshold the capacity reaches a "universal" limit, independent of the degree of disorder. Whether or not this limit is larger or smaller than the capacity without amplification depends on the disorder, as well as on the input power. Explicit expressions are obtained for heterodyne detection of coherent states, and generalized for arbitrary detection scheme.
After propagating through a random amplifying medium, a squeezed state commonly shows excess noise above the shot-noise level. Since large noise can significantly reduce the signal-to-noise ratio, it is detrimental for precision measurement. To circumvent this problem, we propose a noise-reduction scheme using wavefront shaping. It is demonstrated that the average output quantum noise can be effectively suppressed even beyond the shot-noise limit. Both the decrease on amplification strength and the increase on input squeezing strength can give rise to a decrease in the suppressed average quant…
In all practical communication channels, the code word consist of Gaussian states and the measurement strategy is often a Gaussian detector such as homodyning or heterodyning. In this paper we investigate the communication performance using a phase-conjugated alphabet and joint Gaussian detection in an phase-insensitive amplifying channel. We find that a communication scheme consisting of a phase-conjugated alphabet of coherent states and a joint detection strategy significantly outperforms a standard coherent-state strategy based in individual detection. Moreover, we show that the performance…
We demonstrate a fundamental breakdown of the photonic spontaneous emission (SE) formula derived from Fermi's golden rule, in absorptive and amplifying media, where one assumes the SE rate scales with the local photon density of states, an approach often used in more complex, semiclassical nanophotonics simulations. Using a rigorous quantization of the macroscopic Maxwell equations in the presence of arbitrary linear media, we derive a corrected Fermi's golden rule and master equation for a quantum two-level system (TLS) that yields a quantum pumping term and a modified decay rate that is net …
Quantum trade-off coding for bosonic communication
量子信道的折衷容量区域表征了发送方可以通过利用信道的许多独立使用以及相同资源的帮助来向接收方传送经典、量子和纠缠比特的最佳净速率。类似地，当无噪声资源是公共、私有和秘密密钥位时，可以考虑折衷容量区域。在[Phys. Rev. Lett. 108，140501（2012）]，我们确定了纯损耗玻色子信道的这些权衡速率区域，并证明了它们是最优的，只要长期存在的最小输出熵猜想是正确的。此外，我们还表明，与分时策略相比，权衡编码策略的性能增益可能非常显著。在本文中，我们提供了详细的推导结果宣布有，我们扩展这些想法的应用，热化和放大玻色子通道。我们还得出了一个“经验法则”的权衡编码，它决定了如何分配光子的编码策略，如果一个大的平均光子数是可用的通道输入。我们对玻色子放大通道的研究结果也适用于相对论量子信息理论中的“Unruh通道”。
Present-day quantum communication predominantly depends on trusted relays (e.g., quantum repeaters, low-Earth-orbit satellite) connected by optical fiber cables to transmit information. However, recent evidence supports a decades-old concept that quantum entanglement, harnessed by current quantum communication systems, does not necessarily rely on a physical relay medium. In modern quantum communication networks, this trusted relay infrastructure is (1) susceptible to security attacks, (2) limited by the channel capacity, (3) subject to decoherence loss, and (4) expensive to set up. The instan…
Manipulative resonant nonlinear optics: nonlinear interference effects and quantum control of nonlinearity, dispersion, transparency and inversionless amplification in an extended strongly-absorbing inhomogeneously-broadened medium
In an ideal linear amplifier, the output signal is linearly related to the input signal with an additive noise that is independent of the input. The decoherence of a quantum-mechanical state as a result of optical amplification is usually assumed to be due to the addition of quantum noise. Here we show that entanglement between the input signal and the amplifying medium can produce an exponentially-large amount of decoherence in an ideal optical amplifier even when the gain is arbitrarily close to unity and the added noise is negligible. These effects occur for macroscopic superposition states…
The transfer of quantum information through a noisy environment is a central challenge in the fields of quantum communication, imaging and nanophotonics. In particular, high-dimensional quantum states of light enable quantum networks with significantly higher information capacities and noise robustness as compared with qubits. However, although qubit entanglement has been distributed over large distances through free space and fibre, the transport of high-dimensional entanglement is hindered by the complexity of the channel, which encompasses effects such as free-space turbulence or mode mixin…
