中文摘要：

我们发现利用相干制备的三能级原子介质可实现低噪声弱光相位操控.基于两波混频效应,相干制备的原子系统在弱光相位操控方面有许多新特性,例如宽频范围内无损常数相位的实现以及无附加相位的吸收与放大等.通过同时锁定抽运光的光强和双光子失谐,我们发现探测光的吸收为零,且探测光的相位对于频率的变化十分缓慢,因而可以通过选择适当的系统参数在很宽的频率范围内实现无损π相位操控.同时,利用该系统我们可以在单光子水平下实现低噪声、无损的量子相位门,这个系统在光通信和信息处理领域有着重要的应用价值.

英文摘要：

We propose a multifunction phase-shifting manipulator with low noise at a single-photon level, by using a threelevel atomic scheme. This three-level system interacts with a strong pumping field and a weak probe field with a large detuning. Due to this large detuning, two lower states can be coherently prepared prior to the injection of the pump and probe fields. In our configuration, the duration of the pumping field is much longer than that of the probe field.By solving the Heisenberg-Langevin equations of our system under the steady state approximation, we calculate the linear susceptibility of the system and examine the quantum noise properties of the probe field in detail. We show that this scheme, which rests on the process of two-wave mixing with initial atomic coherence, exhibits many interesting properties that neither typical electromagnetically induced transparency（EIT） schemes nor active Raman gain（ARG）schemes possess. Although both EIT- and ARG-based schemes have been widely investigated in atomic medium, the direct generalizations of these schemes to the single/few photon limit prove to be more problematic. The low fidelity due to the significant probe-field attenuation in EIT medium and the large quantum noise due to the amplification of the probe field in an active Raman gain medium are the main obstacles that prohibit a high-fidelity, low-noise phase shifter from being realized in the single/few photon limit. Physically, this scheme can be viewed as a hybrid scheme in which two processes of different physical principles are allowed to interfere with each other to achieve many desired functionalities.For instance, it can be used as a lossless two-photon-broadband phase-shifter with suitable system parameters. It can also be used as an attenuator/amplifier and a total transparency with a zero phase shift. In particular, we show that by locking the pump field intensity and the two-photon detuning simultaneously a flat constant π-phase shift can be realized with unit probe fidelity in a broad