Quantum entanglement of angular momentum states with quantum numbers up to 10010 (1607.00922v1)

Abstract: Photons with a twisted phase front carry a quantized amount of orbital angular momentum (OAM) and have become important in various fields of optics, such as quantum and classical information science or optical tweezers. Because no upper limit on the OAM content per photon is known, they are also interesting systems to experimentally challenge quantum mechanical prediction for high quantum numbers. Here, we take advantage of a recently developed technique to imprint unprecedented high values of OAM, namely spiral phase mirrors (SPM), to generate photons with more than 10,000 quanta of OAM. Moreover, we demonstrate quantum entanglement between these large OAM quanta of one photon and the polarization of its partner photon. To our knowledge, this corresponds to entanglement with the largest quantum number that has been demonstrated in an experiment. The results may also open novel ways to couple single photons to massive objects, enhance angular resolution and highlight OAM as a promising way to increase the information capacity of a single photon.

• The paper demonstrates photon entanglement with angular momentum states up to 10,010 ħ using spiral phase mirrors in a Michelson interferometric arrangement.
• The experimental methodology employs coincidence imaging and superposition measurements to confirm entanglement with high witness values.
• Results challenge traditional quantum-classical boundaries and indicate promising applications in quantum communication and information processing.

Quantum Entanglement of High Angular Momentum States

The paper presented in the paper explores the entanglement of photons with substantial orbital angular momentum (OAM), pushing the experimental boundaries by demonstrating entanglement with quantum numbers exceeding 10,000 ħ. The research utilizes spiral phase mirrors (SPM) to impart these unprecedented OAM values, expanding the potential for photonic systems in both theoretical and practical applications.

Major Findings and Methodology

The researchers succeeded in generating hybrid entangled states by transferring a photon's polarization to a transverse spatial mode with OAM quanta of 500, 1000, and ultimately 10,010 ħ. The system harnesses a Michelson-type interferometric setup, where SPMs serve as the core technology to imprint the desired OAM values onto the photons. This approach enables the generation of entangled states with large quantum numbers, effectively scaling the dimensional capabilities of quantum states. Two key experimental tests confirmed the robustness of the entanglement:

1. Coincidence Imaging: For photons carrying OAM up to 500 ħ, an intensified CCD camera was used in a coincidence-imaging setup. Here, the polarization state of a photon (Alice) triggered the imaging of the OAM profile of its entangled partner (Bob). The entangled state resulted in observable shifts in the paddle-like pattern, indicating a successful entanglement with a witness value of 1.626 ± 0.022.
2. Superposition Measurement: For photons with 1,000 and 10,010 ħ of OAM, the researchers used a spatial mask to approximate the OAM superposition state. The analysis of the shifted extrema in coincidence detection confirmed the entanglements, with respective witness values suggesting non-separability of the states.

Technical Challenges and Solutions

Generating photons with high OAM values presents significant challenges, especially in terms of transfer efficiency and detection. The paper identified several sources of loss, such as the complexity of machining the SPM surface for large l values and the necessity to use only a fraction of the available beam for measurements. The linear approximation of the mode rotation through slit masks for higher OAM values was a practical measure to validate entanglement under these constraints, albeit requiring defect corrections through accidental coincidence subtraction.

Implications and Future Prospects

This research holds considerable implications for both fundamental and applied quantum mechanics. The results challenge the classical predictions regarding the quantum-classical transition, suggesting no apparent transition even at high quantum numbers within the parameters tested. From a practical standpoint, the findings may influence the development of quantum information technologies, particularly in increasing the information capacity of a single photon. The research hints at potential advancements in fields like optical communications and quantum computing, where the spatial degrees of freedom offered by high OAM states could significantly enhance information processing and retention capabilities.

In terms of theoretical contributions, the paper elucidates the coherence of quantum descriptions even under extreme conditions, providing experimental verification against long-standing theoretical conjectures. These large OAM quanta also open novel possibilities for photon-matter interactions, such as coupling photons to macroscopic objects in quantum optomechanical research, offering pathways to explore the transfer of angular momentum at impressively large scales.

In conclusion, this research not only sets a new benchmark for the entanglement of high angular momentum states but also lays the groundwork for future explorations into the scalability of quantum states and their implications in the broader landscape of quantum mechanics and photonics technology.