image: Depiction of quantum levitation exploiting the nonequilibrium Casimir force. A modestly biased semiconductor creates modes that exert a repulsive force on a nearby surface. This force overcomes the attractive equilibrium Casimir force contribution at submicron distances. See Spreng et al., pp. 266–273.
Credit: Optica Quantum
WASHINGTON—The new issue of Optica Quantum is available. A Gold Open Access journal from Optica Publishing Group, Optica Quantum provides a home for high-impact research in quantum information science and technology enabled by optics and photonics.
Summaries of the 12 research articles in the latest issue are provided below.
Sanjukta Kundu, Jerzy Szuniewicz, Grzegorz Firlik, Alexander Krupinski-Ptaszek, and Radek Lapkiewicz, "High-dimensional quantum correlation measurements with an adaptively gated hybrid single-photon camera," Optica Quantum 2, 206-213 (2024).
https://doi.org/10.1364/OPTICAQ.522894
Single-photon cameras, essential for measuring high-dimensional spatial correlations, often face a trade-off between spatial and temporal resolution. A proposed hybrid intensified camera offers multi-megapixel spatial and nanosecond temporal resolution, incorporating in-frame feedback to halt acquisition after detecting a set number of photons. This significantly enhances data acquisition rates, enabling faster measurements of quantum optical phenomena like the spontaneous parametric down-conversion process.
Emanuele Brusaschi, Massimo Borghi, Marcello Bacchi, Marco Liscidini, Matteo Galli, and Daniele Bajoni, “Photon number distribution of squeezed light from a silicon nitride microresonator measured without photon number resolving detectors,” Optica Quantum 2, 214-221 (2024).
https://doi.org/10.1364/OpticaQ.528566
High-Q optical microresonators are bright sources of squeezed light for quantum information processing, sensing and simulation. Most of their performance metrics can be extracted from their photon number distribution, which we reconstruct through the use of standard equipment: two threshold detectors and a variable optical attenuator. Being fast and simple, this characterization procedure is helpful for those who work on squeezed light and do not rely on the use of photon number resolving detectors.
Sheng-Dian Zhang, Jie Wang, Qian Zhang, Ya-Feng Jiao, Yun-Lan Zuo, Şahin K. Özsemir, Cheng-Wei Qiu, Franco Nori, and Hui Jing, "Squeezing-enhanced quantum sensing with quadratic optomechanics," Optica Quantum 2, 222-229 (2024).
https://doi.org/10.1364/OPTICAQ.523480
Incorporating intracavity squeezing significantly enhances the performance of quadratic cavity optomechanical sensors. The force sensitivity can reach (10.2 aN)^2/Hz even at room temperature. This advancement opens new opportunities for ultrahigh sensitivity applications in quantum metrology and fundamental physics tests.
F. W. Knollmann, E. Clements, P. T. Callahan, M. Gehl, J. D. Hunker, T. Mahony, R. McConnell, R. Swint, C. Sorace-Agaskar, I. L. Chuang, J. Chiaverini, and D. Stick, “Integrated photonic structures for photon-mediated entanglement of trapped ions,” Optica Quantum 2, 230-244 (2024).
https://doi.org/10.1364/OPTICAQ.522128
Combining trapped ions with integrated single-photon collection optics, waveguide beam splitters, and integrated detectors offers a promising route to compact remote entanglement modules. This work analyzes trade-offs of possible entanglement schemes and analyze devices designed for their implementation.
Toshiki Matsumoto, Sota Sato, Shota Akei, Yuichiro Nakano, Satoshi Iba, Jun Ishihara, Katsuhiko Miyamoto, Nobuhiko Yokoshi, Takashige Omatsu, and Ken Morita, “Coherent transfer of higher-order polarization state of photons to spin structure state of electrons in a semiconductor,” Optica Quantum 2, 245-253 (2024).
https://doi.org/10.1364/OpticaQ.527615
The coherent transfer from structured light to a structured spin state was achieved using a semiconductor with a V-shaped three-level system. The result opens up the possibility of quantum state transfer from single photons to single electron spins with different degrees of freedom (spin angular momentum and orbital angular momentum), leading to a step toward advanced quantum teleportation and the quantum Internet.
Alexander Miloshevsky, Lucas M. Cohen, Karthik V. Myilswamy, Muneer Alshowkan, Saleha Fatema, Hsuan-Hao Lu, Andrew M. Weiner, and Joseph M. Lukens, “CMOS photonic integrated source of broadband polarization-entangled photons,” Optica Quantum 2, 254-259 (2024).
https://doi.org/10.1364/OpticaQ.521418
A proposed CMOS-fabricated silicon photonic integrated circuit comprises a bidirectionally pumped microring resonator and two polarization splitter-rotators for fully on-chip generation of polarization entangled photons. A broadband source (C+L-band) generates over 100 high-fidelity fully characterized channels. Exploiting this high channel density, we investigate the photon-pair source for flex-grid quantum networking, testing a variety of flexible channel groupings from 2 to 116 and showing the tradeoff between the state fidelity and flux.
Evelyn A. Ortega, Jorge Fuenzalida, Krishna Dovzhik, Rodrigo F. Shiozaki, Juan Carlos Alvarado-Zacarias, Rodrigo Amezcua-Correa, Martin Bohmann, Sören Wengerowsky, and Rupert Ursin, “Implementation of space-division multiplexed entanglement-based quantum cryptography over multicore fiber,” Optica Quantum 2, 260-265 (2024).
https://doi.org/10.1364/OpticaQ.527903
This implementation allows multiple users to share secret key rates with low QBER. The entangled photons are distributed by multicore fiber, whose secret key rates increase according to the number of cores. This new scheme overcomes the key rate limits in quantum communication and paves the way for efficient multi-party quantum communications protocols.
Benjamin Spreng, Calum Shelden, Tao Gong, and Jeremy N. Munday, "Casimir repulsion with biased semiconductors," Optica Quantum 2, 266-273 (2024). https://doi.org/10.1364/OPTICAQ.523360
This work explores systems involving moderately biased semiconductors that exhibit strong repulsive Casimir forces, including quantum levitation enabled by the nonequilibrium Casimir force. A modestly biased semiconductor creates modes that exert repulsive forces on a nearby surface, which overcome the attractive equilibrium Casimir force contribution at submicron distances.
Tim Strobel, Stefan Kazmaier, Tobias Bauer, Marlon Schäfer, Ankita Choudhary, Nand Lal Sharma, Raphael Joos, Cornelius Nawrath, Jonas H. Weber, Weijie Nie, Ghata Bhayani, Lukas Wagner, André Bisquerra, Marc Geitz, Ralf-Peter Braun, Caspar Hopfmann, Simone L. Portalupi, Christoph Becher, and Peter Michler, “High fidelity distribution of triggered polarization-entangled telecom photons via a 36km intra-city fiber network,” Optica Quantum 2, 274-281 (2024).
https://doi.org/10.1364/OpticaQ.530838
Polarization-entangled photons are an important tool in quantum information and communication. Highly entangled photons generated by semiconductor quantum dots can be frequency converted to telecom wavelength and can propagate over 36 km of intra-city-deployed fibers without degrading the entanglement.
Hsuan-Hao Lu, Joseph M. Lukens, Muneer Alshowkan, Brian T. Kirby, and Nicholas A. Peters, “Building a controlled-NOT gate between polarization and frequency,” Optica Quantum 2, 282-287 (2024).
https://doi.org/10.1364/OpticaQ.525837
Leveraging multiple photonic degrees of freedom, a controlled-NOT gate was developed between polarization and frequency using directionally dependent electro-optic phase modulation within a fiber Sagnac loop. The high-fidelity operation, validated through computational basis measurements and the synthesis of all four polarization-frequency Bell states with fidelities over 98%, paves the way for advanced quantum communication protocols utilizing hyperentangled photons.
Danbi Kim, Jiho Park, Changhoon Baek, Sun Kyung Lee, and Han Seb Moon, “Complementarity of which-path information in induced and stimulated coherences via four-wave mixing process from warm Rb atomic ensemble,” Optica Quantum 2, 288-295 (2024).
https://doi.org/10.1364/OpticaQ.528135
This study significantly advances our knowledge of the wave-particle duality in quantum systems, emphasizing the importance of which-path information and its effects on interference, entanglement, and predictability. Through careful manipulation and measurement using entangled photon pairs from independent warm atomic ensembles with a double-path interferometer, the researchers provide valuable insights into the quantum-classical transition.
Amanuel Anteneh, Léandre Brunel, and Oliver Pfister, “Machine learning for efficient generation of universal photonic quantum computing resources,” Optica Quantum 2, 296-302 (2024).
https://doi.org/10.1364/OpticaQ.523445
Field-based photonic quantum computing is a scalable, viable path toward universal, fault-tolerant quantum computing. The next crucial step is developing photonic quantum error correction, requiring specific exotic quantum states that are difficult to generate experimentally. This work achieves a near-100% success rate for the generation of squeezed cat states by using deep reinforcement learning to drive a simple quantum optical loop based on squeezing, interference, and photon-number-resolved detection, requiring only very few iterations.
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Optica Quantum