Squeezed Light Powers Real-Time Quantum Teleportation

by

Author: Denis Avetisyan

Researchers have built a system that generates the essential quantum resources for teleportation using squeezed light and photon subtraction, bringing practical quantum networks closer to reality.

This work demonstrates a real-time heralded resource state generator for non-Gaussian teleportation, leveraging two-mode photon subtraction on squeezed light to advance quantum repeater technologies.

While quantum teleportation relies on entangled states, achieving high fidelity often necessitates resources beyond those offered by conventional squeezed light. This work, titled ‘Real-time heralded non-Gaussian teleportation resource-state generator’, demonstrates an experimental platform for creating heralded, non-Gaussian entangled states in real-time via two-mode photon subtraction. Characterization via homodyne tomography confirms a fidelity of 0.973 ± 0.005 with the target resource state, enabled by a synchronized detection system delivering low-latency heralding signals. Could this advancement pave the way for practical quantum networking protocols, particularly in the context of quantum repeaters and advanced quantum computation?

Beyond Classical Limits: Embracing Quantum Nuance

Conventional quantum teleportation relies heavily on Gaussian states – those described by Gaussian probability distributions – as the resource for entanglement. However, these states inherently impose limitations on the achievable fidelity and the amount of quantum information that can be faithfully transferred. This restriction stems from the fundamental properties of Gaussian states, which lack the necessary quantum correlations to fully exploit the potential of entanglement for teleportation. Specifically, Gaussian states are susceptible to noise and decoherence, leading to errors in the reconstructed quantum state at the receiving end. The inherent smoothness of Gaussian distributions also limits their ability to encode complex quantum information, hindering the capacity for high-dimensional quantum communication and computation. Consequently, surpassing the constraints of Gaussian states is crucial for realizing the full promise of quantum teleportation and its applications in secure communication and distributed quantum computing.

Quantum teleportation, while theoretically sound, historically relies on Gaussian states, which impose fundamental limits on the fidelity and efficiency of information transfer. Recent advancements explore the potential of non-Gaussian entanglement to overcome these restrictions, and a promising technique involves photon subtraction – a process of removing a photon from an entangled state to reshape its quantum properties. Researchers have demonstrated that by employing this method, the generated entangled state achieves a log negativity of $0.52 \pm 0.03$, a key indicator of entanglement strength exceeding the bounds achievable with Gaussian states. This improvement signifies a tangible step toward more effective quantum communication protocols and the potential to bolster the performance of quantum computational tasks by enhancing the reliability of state transfer.

The advancement of quantum teleportation beyond the constraints of Gaussian states promises a significant leap toward more resilient quantum communication and computation. By harnessing the unique properties of non-Gaussian entanglement, systems can overcome limitations inherent in traditional protocols, potentially enabling the reliable transmission of quantum information over extended distances and through noisy channels. This enhanced robustness is crucial for building practical quantum networks, where maintaining the integrity of quantum states is paramount. Furthermore, the ability to create and manipulate highly entangled, non-Gaussian states could unlock new avenues in quantum computation, potentially facilitating algorithms and processes that are intractable for classical computers or those relying on Gaussian-state quantum systems. The increased fidelity and efficiency afforded by this approach are not merely incremental improvements, but rather foundational steps toward realizing the full potential of a quantum future.

Achieving reliable quantum teleportation beyond classical limits is critically dependent on the meticulous preparation and maintenance of entangled states, alongside robust phase stabilization techniques. Entangled photons, the cornerstone of this process, are exceptionally sensitive to environmental noise and imperfections in optical components, which can rapidly degrade the quality of the entanglement and introduce errors. Precise control over the generation, manipulation, and detection of these states is therefore paramount; even minor deviations from ideal conditions can significantly reduce teleportation fidelity. Furthermore, maintaining a stable phase relationship between the entangled photons is essential, requiring active feedback loops and careful calibration to counteract phase drifts caused by temperature fluctuations or mechanical vibrations. Successful implementations necessitate advanced experimental setups and sophisticated control algorithms to ensure the preservation of quantum coherence and maximize the efficiency of the teleportation protocol.

Harnessing Squeezed Light: The Foundation of Non-Gaussian States

Two-mode squeezed vacuum (TMSV) states are a critical resource for non-Gaussian teleportation protocols due to their unique quantum correlations. These states, denoted as $|Ψ\rangle = \frac{1}{\sqrt{2}}(|00\rangle + |11\rangle)$, exhibit reduced noise in one quadrature of the electromagnetic field at the expense of increased noise in the orthogonal quadrature. The degree of squeezing, quantified by the amount of noise reduction, directly impacts the fidelity of the teleportation process. High-quality TMSV states necessitate minimal loss, precise phase matching between the entangled photons, and suppression of extraneous modes to maintain the integrity of the quantum correlations and enable efficient non-Gaussian state transfer. The generation of these states forms the basis for encoding and transmitting quantum information in our teleportation scheme.

The generation of high-quality two-mode squeezed vacuum (TMSV) states requires a Squeezed Light Source actively stabilized using Pound-Drever-Hall (PDH) control. This feedback mechanism locks the optical cavity length to the frequency of a reference laser, minimizing fluctuations caused by thermal and mechanical noise. Specifically, the PDH technique maintains resonance, maximizing the circulating power within the cavity and thus enhancing the squeezing effect. The resulting reduction in quantum noise, particularly in the amplitude quadrature, is critical for achieving high degrees of entanglement between the generated modes, as any added noise degrades the fidelity of the TMSV state and reduces the achievable log negativity.

To counteract signal loss inherent in optical systems and maintain sufficient signal-to-noise ratio for efficient quantum information processing, optical amplifiers are integrated into the TMSV generation setup. These amplifiers are specifically chosen and operated to minimize added noise that would degrade the entanglement quality. Critical to this process is preserving the quantum properties of the squeezed vacuum state; therefore, amplifiers with low noise figures and carefully controlled gain are employed. Performance characterization confirms that the amplification process introduces minimal excess noise, ensuring that the resulting TMSV state retains high degrees of entanglement, as quantified by metrics such as log negativity.

Generalized photon subtraction techniques were implemented to increase the non-Gaussian characteristics of the two-mode squeezed vacuum state. This process builds upon standard photon subtraction by allowing for more complex operations on the quantum state. Experimental results demonstrate a log negativity of $0.49 \pm 0.03$ for states with zero photons subtracted and $0.52 \pm 0.03$ for states with one photon subtracted, quantifying the degree of entanglement and non-classicality achieved through this method.

Precision Control: Stabilizing the Quantum Fabric

Maintaining a stable phase relationship between optical components is achieved through a suite of advanced phase stabilization techniques. These techniques are critical because even minor phase deviations can significantly degrade the quality of quantum states and interfere with precise measurements. The system employs active feedback loops that continuously monitor and correct for phase drift, utilizing error signals derived from comparison with a stable reference. This process minimizes phase noise and ensures the consistent interference required for coherent quantum operations. Specifically, the implemented methods address both common-mode and differential phase errors, allowing for high-precision control over the relative phase of optical signals throughout the experiment.

Error signal feedback forms a critical component of maintaining system stability and achieving optimal performance in quantum coherence experiments. Deviations from the desired operational parameters, such as phase or amplitude fluctuations, are continuously monitored and quantified to generate an error signal. This signal is then used to actively correct the system, typically through actuators controlling optical components. The feedback loop minimizes these deviations, effectively reducing noise and improving the fidelity of quantum state manipulation. The precision of this correction is directly linked to the accuracy and bandwidth of the error signal generation and the responsiveness of the corrective actuators, enabling high-stability control necessary for sensitive quantum operations.

Lock-in detection and sideband generation are implemented to mitigate the effects of phase drift on optical signals. Sideband generation introduces a known frequency modulation onto the carrier signal, creating predictable sidebands whose phase is sensitive to drift. Lock-in detection then isolates and amplifies signals at these specific sideband frequencies, effectively filtering out noise and allowing for precise measurement of the phase shift. This technique enables the system to discern even minute changes in phase, on the order of fractions of a wavelength, and subsequently apply corrective adjustments to maintain system stability and signal fidelity. The resulting phase measurements are used in feedback loops to actively stabilize the optical path length and counteract drift caused by environmental factors or component variations.

Real-time synchronization across the quantum system is managed by Field-Programmable Gate Array (FPGA) control systems. These systems distribute precise timing signals via Radio Frequency over Fiber (RFoF) distribution networks, ensuring coordinated operation of all components. This synchronization enables a heralded signal jitter of $91 \pm 1$ ns, a critical parameter for maintaining the fidelity of quantum state transfer and measurement. The FPGA control layer dynamically adjusts timing based on system feedback, compensating for propagation delays and component variations within the RFoF network to achieve this level of precision.

Verifying Fidelity: A Glimpse into Quantum State Reconstruction

Determining the success of quantum teleportation hinges on precisely characterizing the reconstructed quantum state at the receiver. To achieve this, researchers utilize Homodyne Detection, a technique sensitive enough to measure the continuous quadratures of the electromagnetic field. This process doesn’t directly reveal the quantum state, but instead provides a statistical distribution of measurement outcomes, from which key properties can be inferred. By repeatedly measuring these quadratures and reconstructing the quantum state through a mathematical process called tomography, it becomes possible to quantify how faithfully the original quantum information has been transferred. The precision of this measurement is paramount; even small errors in state characterization can obscure improvements gained through advanced techniques like non-Gaussian entanglement, ultimately limiting the potential of quantum communication and computation.

Dual-homodyne detection represents a powerful technique for fully reconstructing the quantum state following teleportation, going beyond simple measurements to provide a complete picture of its properties. This method involves measuring the quadratures of the electromagnetic field, effectively capturing both amplitude and phase information, and allowing researchers to determine the density matrix that describes the state. By comparing this reconstructed density matrix with the original state, a quantifiable metric – teleportation fidelity – can be calculated. This fidelity, representing the degree of similarity between the input and output states, is crucial for assessing the success of the teleportation protocol and verifying that the quantum information has been faithfully transferred. The comprehensive nature of dual-homodyne detection therefore doesn’t just confirm whether teleportation occurred, but also provides detailed insights into how well it performed, enabling precise optimization of quantum communication systems.

Recent measurements decisively demonstrate the advantages of utilizing non-Gaussian entanglement in quantum teleportation protocols. Through the strategic subtraction of photons from an entangled state, researchers observed a quantifiable improvement in the log negativity – a key metric for assessing entanglement – registering a gain of 0.03. This enhancement signifies a stronger, more resilient entangled resource capable of faithfully transferring quantum information. The observed increase in log negativity directly correlates with a higher degree of entanglement, ultimately leading to improved teleportation fidelity and bolstering the potential for more secure and efficient quantum communication networks. This result highlights the power of tailoring entangled states to optimize performance in practical quantum technologies.

The enhancement in teleportation fidelity, achieved through optimized entanglement resources, signifies a crucial step towards practical quantum technologies. Increased fidelity directly translates to a reduced error rate in transmitting quantum information, bolstering the reliability of quantum communication networks. This improvement isn’t merely incremental; it allows for the implementation of more complex quantum algorithms and protocols that are inherently sensitive to noise and errors. Consequently, these advancements enable the development of more robust quantum computation schemes, where fragile quantum states can be manipulated with greater precision and for extended durations. Ultimately, this work contributes to realizing the full potential of quantum information processing, opening doors to secure communication, powerful computation, and advanced sensing capabilities previously unattainable with classical systems.

The pursuit of quantum networking, as demonstrated by this real-time heralded resource state generator, echoes a fundamental principle of efficient communication: distilling signal from noise. This work, focused on two-mode photon subtraction from squeezed light, actively removes unnecessary quantum correlations to enhance teleportation fidelity. It is a testament to the power of subtraction as a refining process. As Richard Feynman once stated, “The first principle is that you must not fool yourself – and you are the easiest person to fool.” This research embodies that honesty, relentlessly stripping away complexity to reveal a more robust and practical pathway towards entanglement distillation and, ultimately, a functioning quantum internet. The elegance lies not in what is added, but in what is skillfully removed.

Beyond the Horizon

The demonstration of a heralded resource state generator, while a necessary step, does not obviate the inherent challenges of scalable quantum networking. The current reliance on two-mode photon subtraction, though effective, introduces loss – an endemic inefficiency in optical systems. Future iterations must address this through alternative, high-fidelity methods for generating the requisite non-Gaussian states, or accept a fundamental limitation on repeater distances. The pursuit of perfection in state generation is, predictably, asymptotic.

Furthermore, the practical implementation of entanglement distillation, crucial for extending network range, remains a significant hurdle. The fidelity of the generated states, even when heralded, is not yet sufficient to guarantee reliable long-distance quantum communication without substantial overhead in error correction. It is a matter of simple geometry: increased complexity does not equate to increased robustness.

The next logical progression lies not simply in improving existing techniques, but in exploring fundamentally different approaches to encoding and transmitting quantum information. The current emphasis on photon polarization, while convenient, may prove to be a local optimum. Clarity, after all, is compassion for cognition, and a more elegant, inherently robust solution likely exists, obscured only by the inertia of established paradigms.

Original article: https://arxiv.org/pdf/2512.08429.pdf

Contact the author: https://www.linkedin.com/in/avetisyan/

See also:

2025-12-11 00:10