Quantum: Ultrastable heterodyne quantum information

“超稳外差量子信息”的提出是为了支持弗吉尼亚大学物理系量子光学和量子信息(QOQI)小组的活动而提出的更新要求。量子信息的基础是使用量子力学的数学公理来处理、存储和传输信息。人们预计这种方法会带来几个好处。首先，对于某些问题，量子计算可以比经典计算产生指数级的加速比，比如费曼预测的模拟量子系统，肖尔预测的因式分解整数。此外，量子密钥分发还为密码学带来了完全的防窃听安全性。在实验上实现量子计算机面临着严峻的挑战。一方面，人们需要可伸缩性，即大量的量子逻辑单元(如果是二进制的话是“量子比特”，如果是多态的话是“量子比特”)，所有这些都是可单独寻址的，并且能够成对地相互作用而成为纠缠。另一方面，人们需要严格控制这种相互作用，并将其限制在量子比特或量子比特上，以避免退相干，这是一种类似测量的不可逆随机演化，由量子寄存器与环境相互作用而产生，环境是量子系统的储存库。自发辐射是原子退相干的一个例子。这个项目致力于量子信息的全光实现。光由于其极弱的(光子-光子)相互作用，具有显著的抗消相干性。反过来，这可能会给产生量子纠缠(上述成对相互作用)带来困难，但这个问题可以通过使用成熟和更加复杂的非线性光学技术来解决，在我们的情况下，使用由光学参数振荡器(OPO)发射的类似激光的高度空间和时间相干的光束。OPO在量子信息，特别是量子通信方面的潜力是众所周知的，但仍远未得到充分开发。该方案的实验方法是将超高分辨率激光光谱学和时频计量学的原理和技术与非线性和量子光学的原理和技术结合起来。这一提议旨在将经典信号处理技术扩展到量子领域，特别是通过使用频域编码量子位数并实现“量子多路复用”，这是调频与调幅无线电信号的量子光学版本。这将通过最先进的相位稳定和频率稳定的OPO来实现，随后将能够通过隐形传态或直接纠缠在不同类型的物理量子之间传输量子信息，例如碱原子(量子存储器)或光纤中的光子(量子总线)。我们还讨论了基于量子比特的密集编码在超灵敏光学测量中的应用。拟议工作的广泛影响包括对UVA物理学研究生项目的积极贡献，五名学生直接提供研究建议，每年几个系研讨会，以及由P.I.于2005年春天创建的新的高级课程“量子光学和量子信息”(物理888)。此外，本科生定期加入到不同水平的研究工作中，包括研究生研究。还包括与UVA工程学院的合作努力，以促进跨部门研究。最后，更广泛地传播研究成果包括与数学系合作在弗吉尼亚大学组织跨学科会议。P.I.在2003年5月联合组织了一次这样的会议，名为“编码理论和量子计算”，并计划在不久的将来重申。

The proposal "Ultrastable heterodyne quantum information" is a renewal request to support theactivity of the Quantum Optics and Quantum Information (QOQI) group in the Physics Department of the University of Virginia (UVa).The foundation of quantum information is the use of the mathematical axioms of quantum mechanics to process, store, and transmit information. One expects several benefits from such an approach. First and foremost, quantum computing can yield an exponential speedup over classical computation for certain problems, such as predicted by Feynman for simulating quantum systems and by Shor for factoring integers. Moreover, quantum key distribution also brings complete security against eavesdropping to cryptography.Daunting challenges face attempts at experimentally realizing a quantum computer. On the one hand, one needs scalability, i.e. a large number of quantum logic units ("qubits" if binary ones or "qudits" if multi-state ones), all individually addressable and able to interact pairwise to become entangled. On the other hand, one needs this interaction to be strictly controlled and limited to the qubits or qudits, in order to avoid decoherence, which is the measurement-like, irreversible random evolution that results from interaction of a quantum register with the environment, a reservoir of quantum systems. Spontaneous emission is an example of decoherence for atoms.This project is dedicated to all-optical implementation of quantum information. Light has remarkable resistance to decoherence, due to its extremely weak (photon-photon) interaction. This, is turn, may present a difficulty for generating quantum entanglement (aforementioned pairwise interactions) but this problem is solved by the use of the mature and ever more sophisticated techniques of nonlinear optics and, in our case, of the laser-like, highly spatially and temporally coherent optical beams emitted by the optical parametric oscillator (OPO). The potential of OPO's for quantum information and, in particular, quantum communication, is very well known but is still far from having been fully exploited. The experimental approach of the proposal is centered on marrying the principles and techniques of ultra-high resolution laser spectroscopy and time-frequency metrology to those of nonlinear and quantum optics. This proposal aims at extending classical signal processing techniques into the quantum domain, in particular by using the frequency domain to encode the qudits and realize "quantum multiplexing," a quantum optical version of FM versus AM radio signals. This will be realized with state-of-the-art phase- and frequency-stabilized OPO's and will subsequently enable the transfer of quantum information, by teleportation or direct entanglement, between different types of physical qudits, such as alkali atoms (quantum memory) or photons in optical fibers (quantum bus). Applications of qudit-based dense coding to ultrasensitive optical measurements impossible with qubits are also discussed.Broader impacts of the proposed work comprise an active contribution to the UVa Physics graduate program, with the direct research advising of five students, of several Departmental seminars per year, and of a new advanced course "Quantum Optics and Quantum Information" (Phys 888), which was created in the spring of 2005 by the P.I. In addition, undergraduate students are periodically joining in the research effort at various levels, including graduate research. Also included are collaborative efforts with UVa Engineering faculty to foster cross-Departmental research. Finally, broader dissemination of research results includes the organization of interdisciplinary conferences at UVa, in association with the Department of Mathematics. The P.I. co-organized one such conference, "Coding Theory and Quantum Computing," in May 2003 and has plans to reiterate in the near future.