In the second part of our review (for the first part see quant-ph/0108080), we discuss a physical model for generation of "truncated" coherent and squeezed states in finite-dimensional Hibert spaces.
Quantum-optical states in finite-dimensional Hilbert space. I. General formalism
近年来,随着量子计算、量子光学态制备和测量技术的发展,特别是离散量子态层析成像技术的发展,人们对有限维希尔伯特空间中量子光学态的研究产生了浓厚的兴趣。在第一部分中,我们提出了两种本质上不同的方法来定义谐振子在有限维希尔伯特空间的状态。其中之一与Pegg、Phillips和Barnett的截断方案有关[Phys. Rev. Lett. 81,1604(1998)] --所谓的量子剪刀装置。第二种方法对应于Leobranski和Tanabranski的截断方案[Phys.Rev.A49,R20(1994)]。我们提出了一些新的定义,这些截断方案有关的状态,并找到他们的明确形式的Fock表示。我们讨论了相干态、相位相干态、位移数态、薛定谔猫和压缩真空的有限维推广。我们展示了一些有趣的性质的状态的帮助下的离散维格纳函数。
Recently, quantum contextuality has been proved to be the source of quantum computation's power. That, together with multiple recent contextual experiments, prompts improving the methods of generation of contextual sets and finding their features. The most elaborated contextual sets, which offer blueprints for contextual experiments and computational gates, are the Kochen--Specker (KS) sets. In this paper, we show a method of vector generation that supersedes previous methods. It is implemented by means of algorithms and programs that generate hypergraphs embodying the Kochen-Specker property …
Interferometry is one of the central organizing principles of optics. Key to interferometry is the concept of optical delay, which facilitates spectral analysis in terms of time-harmonics. In contrast, when analyzing a beam in a Hilbert space spanned by spatial modes -- a critical task for spatial-mode multiplexing and quantum communication -- basis-specific principles are invoked that are altogether distinct from that of `delay.' Here, we extend the traditional concept of temporal delay to the spatial domain, thereby enabling the analysis of a beam in an arbitrary spatial-mode basis -- exempl…
Coherent states in a projected Hilbert space have many useful properties. When there are conserved quantities, a representation of the entire Hilbert space is not necessary. The same issue arises when conditional observations are made with post-selected measurement results. In these cases, only a part of the Hilbert space needs to be represented, and one can define this restriction by way of a projection operator. Here coherent state bases and normally-ordered phase-space representations are introduced for treating such projected Hilbert spaces, including existence theorems and dynamical equat…
The four-component cat state represents a particularly useful quantum state for realizing fault-tolerant continuous variable quantum computing. While such encoding has been experimentally generated and employed in the microwave regime, the states have not yet been produced in the optical regime. Here we propose a simple linear optical circuit combined with photon counters for the generation of such optical four-component cat states. This work might pave the way for the first experimental generation of fault-tolerant optical continuous variable quantum codes.
Development of quantum computation and communication, recently shown to be supported by contextuality, arguably asks for a requisite supply of contextual sets. While that has been achieved in even dimensional spaces, in odd dimensional spaces only a dozen contextual critical Kochen-Specker (KS) sets have been found so far. In this paper we give three methods for automated generation of arbitrarily many contextual KS and non-KS sets in any dimension for possible future application and implementation and we employ them to obtain millions of KS and other contextual sets in dimensions 3, 5, 7, and…
Hilbert Space Black Hole Analog: Unidirectional Transport without Driving
Tulane University(杜兰大学);Akhiezer Institute for Theoretical Physics, NSC KIPT(阿赫谢泽理论物理研究所,NSC KIPT);Technische Universität Dresden(德累斯顿工业大学);Jet Propulsion Laboratory, California Institute of Technology(加州理工学院喷气推进实验室)
We present an optical design where polarization-entangled photon pairs are generated within two $β$-Barium Borate crystals whose optical axes are parallel. This design increases the spatial mode overlap of the emitted photon pairs enhancing single mode collection without the need for additional spatial walk-off compensators. The observed photon pair rate is at least 65000 pairs/s/mW with a quantum state fidelity of 99.53$\pm$0.22% when pumped with an elliptical spatial profile.
Positive operator valued measurements (POVMs) play an important role in efficient quantum communication and computation. While optical systems are one of the strongest candidates for long distance quantum communication and information processing, efficient methods to implement POVMs in these systems are scarce. Here we propose an all-optical scheme to implement an arbitrary POVM using linear optical components on m-dimensional Hilbert space of internal degrees of freedom. Linear optical nature of the proposed scheme makes it efficient and robust. We show how the scheme can be applied for state…
Entangling the optical frequency comb: simultaneous generation of multiple 2x2 and 2x3 continuous-variable cluster states in a single optical parametric oscillator
We propose quantum-mechanical model of a beam splitter with second-order nonlinearity and show that non-classical features such as squeezing and sub-Poissonian photon statistics of optical fields can be generated in output fundamental and second harmonic modes when we mix coherent light beams via such a nonlinear beam splitter.
In nonrelativistic quantum mechanics the spontaneous generation of singularities in smooth and finite wave functions, is a well understood phenomenon also occurring for free particles. We use the familiar analogy between the two-dimensional Schroedinger equation and the optical paraxial wave equation to define a new class of square-integrable paraxial optical fields which develop a spatial singularity in the focal point of a weakly-focusing thin lens. These fields are characterized by a single real parameter whose value determines the nature of the singularity. This novel field enhancement mec…
Many theories of quantum gravity, as string theory, loop quantum gravity, and doubly special relativity, predict the existence of a minimal length scale and outline the need to generalize the uncertainty principle. This generalized uncertainty principle relies on modified commutation relations that - if applied to the second quantization - imply an excess energy of the electromagnetic quanta with respect to $\hbar ω$. Here we show that this "dark energy of the photon" is amplified during nonlinear optical process. Therefore, if one accepts the minimal length scenario, one must expect to observ…