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Immagine del redattoreAndrea Viliotti

Quantum Teleportation in Optical Fiber: Coexistence with 400 Gbps Communications

The research paper “Quantum teleportation coexisting with classical communications in optical fiber” by Jordan M. Thomas, Fei I. Yeh, and Jim Hao Chen, conducted with the involvement of various research centers, including Northwestern University, investigated the operation of quantum teleportation over 30.2 km of optical fiber carrying a conventional 400 Gbps optical signal. The goal was to assess whether a quantum state could be transferred over distance without compromising the classical network. The test confirms that even with high power levels in the C-band, fidelity remains reliable, opening prospects for integrating quantum functions into already operational infrastructures.

Quantum Teleportation in Optical Fiber
Quantum Teleportation in Optical Fiber: Coexistence with 400 Gbps Communications

Quantum Teleportation and High-Speed Optical Fiber Synergy

Quantum teleportation in optical fiber and high-speed optical communications are crucial for the development of future networks. In the experiment described here, the researchers transferred the state of a photon from one node to another, exploiting entanglement generated at a second node. This process takes place while the same fiber carries an optical channel capable of transmitting 400 Gbps in the C-band. With a Bell measurement, the initial photon is destroyed together with one of the two entangled photons, projecting the remaining photon into the desired state. Tests confirm that quantum teleportation and optical communications can coexist without significant compromise, ensuring high fidelitym. Cobining quantum signals and high-power light usually encounters limits due to noise generated by inelastic scattering, such as SpRS (Spontaneous Raman Scattering).


If the quantum photons have very low intensity, it becomes crucial to place them at wavelengths that maximize the probability of distinguishing true signals from noise. In this research, photons are placed in the O-band at 1290 nm, a choice aimed at reducing the Raman effect, which is more pronounced when signals and quantum photons lie too close in frequency. Supporting this strategy, the researchers inserted highly selective spectral filters in front of the detectors. It emerged that even with peak powers well above the minimum required to carry 400 Gbps (about 0.5 mW), the noise level remains manageable through temporal coincidence windows and optical filtering, allowing nearly all spurious counts not correlated to the quantum signal to be discarded.


In practice, the 1290 nm quantum photons travel in the opposite direction of the classical light in the fiber, or co-propagate depending on the section, yet remain associated with a channel where classical power does not significantly alter entanglement. The coherence of the photons is essential for the so-called Hong-Ou-Mandel interference, an effect that reveals the quantum nature of light by measuring how two photons overlap indistinguishably on a beam splitter. It was observed that the interference visibility remains above 80%, far beyond the 50% threshold typical of the classical regime. Experimentally, the concept of teleportation is confirmed when the target photon, located in a distant laboratory, takes on the state prepared by another laboratory, without the need to directly transmit the original photon.


A particularly noteworthy result is that classical power can exceed the minimum required by the conventional system hundreds of times over without causing quantum teleportation fidelity to collapse. For businesses, this opens up the possibility of using existing optical network segments to implement, in parallel with traditional data flows, a quantum transport function. This approach allows a significant reduction in infrastructure costs, avoiding the need to install dedicated cables or compromise network performance. Tests conducted over 30.2 km of fiber, operating with power up to 74 mW, demonstrate that conventional data transmission can be scaled to capacities of several terabits per second while preserving the possibility of transferring a quantum state without degradation.


Reducing Raman Noise in Quantum Teleportation Experiments

The researchers used two photon sources configured via spontaneous parametric conversion in lithium niobate waveguides: one to produce heralded single photons (i.e., with a detector signaling the actual emission of a photon in the other line), the other to create polarization-entangled photon pairs. The initial tests focused on the stability of these sources and their efficiency in counteracting noise generated by a 400 Gbps transceiver operating at 1547.32 nm. This device, provided by Ciena Corporation, works with power ranging from the minimum values just enough to establish the connection up to 74 mW launched into the 30.2 km fiber section. These 30.2 km are coiled on a spool inside a laboratory at Northwestern University, then connected by another 48 km of deployed fiber carrying the classical signal to the Chicago campus, for a total of 78.2 km.One of the key factors enabling noise containment is the decision to generate quantum photons in the O-band at around 1290 nm. This technique reduces the likelihood that C-band signals, which can reach tens of mW in the fiber, produce noise photons at the quantum channel wavelengths. To further optimize signal cleanliness, the researchers employed Bragg grating filters (FBG) just 60 pm wide.


These filters narrow the photons’ spectrum and increase their coherence, a crucial condition for ensuring that interference between two photons from different sources can be unambiguously verified. In addition, the use of superconducting nanowire single-photon detectors (SNSPD) with over 90% efficiency and very low dark count rates facilitates the observation of correlated events.Teleportation is then made possible by the entanglement on one of Bob’s channels. When Alice’s photon (the qubit to be teleported) and one of Bob’s photons (from an entangled pair) undergo a Bell measurement (BSM) in an intermediate station, Bob’s remaining photon is projected into the same initial state prepared by Alice. The output from the BSM corresponds to a projection that requires complete spectral and temporal indistinguishability of the two photons incident on the beam splitter: hence the importance of tight synchronization and identical emission profiles. The latter aspect depends on pumping the lithium niobate waveguides, controlled with temporal amplitude modulation on the order of 65 ps.


Bell measurements, among other things, rely on polarization optics that separate photons into orthogonal horizontal/vertical states, followed by counting coincidences in the time domain. This procedure is sensitive to the presence of noise photons, which is why, in the experimental architecture, an O/C-band multiplexer almost completely rejects the C-band light, isolating the 1290 nm from the broad power of the classical signal. Each time photon coincidences are detected at the Bell measurement detectors, an event is recorded to reconstruct the final state measured at Bob’s location. This reconstruction, performed via tomography, shows the fidelity with which the state sent by Alice arrived intact at its destination, irrespective of the network traffic present in the fiber.


Fidelity and Interference in Quantum Teleportation over Optical Fiber

To evaluate the quality of entanglement distribution and the ability to handle interference between Alice’s and Bob’s photons, visibility measurements were taken under various power scenarios. Without a classical signal in the fiber, the experiment had already reached a Hong-Ou-Mandel visibility of about 82.9%. Introducing C-band power levels of 74 mW results in a value of around 80.3%, which is comfortably above the limit that characterizes purely classical interference.


Hence, the coexistence process has a limited impact and does not undermine the ability to carry out the quantum operation.The researchers then tested the effectiveness of genuine teleportation. In particular, when the qubit is polarized horizontally or vertically, fidelity approaches values around 95–97%, indicating that the states are transferred with excellent correspondence to their initial forms. For diagonal or anti-diagonal states, fidelity is slightly lower, though still in the 85–87% range. Across the entire Bloch sphere, an average fidelity of about 90% is achieved, far above the 2/3 threshold indicative of purely classical processes or classical correlations.All these indicators show how quantum interference — an essential element for Bell measurements and teleportation — is preserved despite the presence of powerful C-band signals. The quality of entanglement on the link connecting Bob to the measurement station also remains consistent, with measured visibilities exceeding 95%, confirming the absence of irrecoverable degradation due to noise. The configuration that boosts classical powers well beyond the minimal necessary level suggests the possibility of hosting multiple conventional channels in parallel, at potential aggregate speeds of several terabits/s, without annihilating the quantum component.


From a managerial and entrepreneurial standpoint, these figures indicate a real opportunity: setting up a hybrid network in which traditional telecom services in the C-band coexist alongside quantum teleportation and entangled-state sharing protocols. This might be attractive to sectors interested in quantum security, cryptography based on quantum key distribution, or future forms of distributed computing. The fact that classical bandwidth resources do not have to be relinquished reduces potential conflict between the two signal forms and, on the other hand, encourages the idea of cohabiting conventional hardware and quantum instrumentation within the same fiber cable.


Integrating Quantum Memories into Teleportation Networks

A topic the researchers focused on is the possibility of integrating quantum memories into network nodes to keep the target photon available while waiting for the outcome of the Bell measurement. This function can be essential in protocols that require physical availability of the teleported state before it can be processed or measured. If classical power can reach hundreds of mW in large optical backbones, it is crucial that the memories tolerate any slight delays and loss processes in the channel. The results obtained with superconducting nanowire detectors suggest that some amount of additional attenuation, if associated solely with losses and not with extra noise, may not dramatically affect fidelity, provided the detectors maintain a low rate of spurious counts.


On the other hand, if the memory also introduces significant intrinsic noise, tolerance margins decrease, since the coincidence window may accumulate spurious counts much more critical than a simple drop in intensity. In such cases, integrating teleportation and memories may require even more selective design of the O-band channel, with filters and amplifiers strategically placed along the route. There is also the possibility that, over longer distances, lower attenuation in the C-band could appear advantageous, but at the cost of higher Raman background noise. In that scenario, one would have to reassess the balance between signal loss and noise. Some future research lines aim specifically to verify whether the optimal parameters change when quantum photons are sent over hundreds of kilometers, potentially with hundreds of mW of classical power and intermediate amplification strategies.Another direction for development concerns the possibility of performing entanglement swapping, a mechanism that creates entanglement between photons originally produced at different sources.


Since teleportation relies on the same principles, being able to concatenate multiple nodes where Bell measurements take place would effectively interconnect quantum resources on a larger scale. This evolution has implications for future optical networks, in which quantum repeaters would be indispensable for overcoming signal attenuation and spreading the availability of entangled states. If the tests in this research confirm the compatibility of teleportation with a robust classical signal, the same scheme, suitably adapted, could also transfer entanglement swapping protocols over a shared infrastructure.


Hybrid Networks: Industrial Opportunities with Quantum Teleportation

Demonstrating that teleportation works while a 400 Gbps channel travels in the same fiber suggests scenarios of great interest from a business perspective. Telecommunications backbones tend to operate with multiple channels in the C-band, often boosted by amplifiers and multiplexing devices: an evolution of this demonstration could lead to metropolitan or regional networks where O-band frequencies are reserved for quantum signals, enabling companies to provide both high-capacity traditional services and new entangled exchange and teleportation services on the same physical medium.Adopting a hybrid network entails some initial costs related to the instrumentation needed for single-photon generation and detection, as well as for the management of quantum memories or frequency conversion if required.


Nevertheless, leveraging the same C-band infrastructure is more advantageous than a fully dedicated system, because it avoids laying additional cables and organizing exclusively quantum pathways. The demonstrated robustness against noise shows that, with careful selection of wavelengths, quantum processes withstand the disturbances accompanying conventional flows, even at high power. In a context of growing demand for cloud services and ultra-high-speed connectivity, the possibility of adding quantum functions to the existing backbone could lead to new business models based on cryptographic solutions or secure remote computing.From a more specialized standpoint, the availability of teleportation connects to the idea of “distributed quantum computing”: if multiple quantum computing nodes were enabled to exchange entangled states, protocols could be developed in which algorithm execution is coordinated across geographically distant resources. The coexistence tested here does not solve every technical challenge, but it shows that advanced quantum protocols do not collapse under the pressure of strong classical optical signals, as long as there is a minimum level of planning for transmission bands. In the future, this could become a competitive advantage for entities capable of integrating classical and quantum services into a single backbone.


Conclusions

The ability to implement quantum teleportation in optical fiber alongside conventional optical traffic opens up significant possibilities for the broader adoption of quantum computing technologies in a variety of application contexts. An optical network that simultaneously supports high-speed classical data and teleportation operations can offer hybrid solutions in which distributed computing resources — such as quantum processors and specialized memories — communicate over existing links, reducing the need for costly dedicated infrastructure. For the data center sector, access to integrated quantum functionalities could facilitate handling complex tasks with shorter response times, triggering an ecosystem where classical and quantum nodes collaborate closely, each leveraging the form of computing best suited to the problem at hand. In cybersecurity, the coexistence of quantum and traditional transmissions within a single network enables advanced forms of cryptography, potentially integrated with quantum consensus algorithms, also applicable to consortial blockchains where authenticity and confidentiality must be guaranteed to a large number of participants. With teleportation available, it would theoretically be possible to orchestrate verification and key-exchange strategies among multiple nodes without jeopardizing normal data communications.


Such an approach could pave the way for solutions in which the robustness of classical networks is combined with the security guarantees of quantum protocols, avoiding a radical overhaul of the infrastructure.Regarding super-accelerated computing, the ability to effectively distribute quantum states over long-distance infrastructures allows for scenarios of “extended supercomputing”: different computing centers, connected to quantum processors, might collaborate in near real-time via hybrid links. The possibility of sharing entanglement and exploiting teleportation lays the groundwork for distributed quantum computing networks, where computational power is enhanced not just by the sum of resources but also by the intrinsic properties of quantum states. If businesses and service providers succeed in integrating these technologies into their data centers, they could create scalable platforms capable of dynamically switching between classical and quantum computing depending on requirements, managing large data volumes with an efficiency still unimaginable today.


The scenario outlined does not eliminate the remaining complexities: further developments are needed in quantum memories, error-correction protocols, and frequency-conversion devices that reduce noise and adapt signals to different routes. Nevertheless, demonstrating the coexistence of strong classical signals and quantum teleportation processes suggests that the standard optical fiber used for conventional communications can become the launch pad for multiple innovative services: from advanced data protection to cryptographic key exchange, all the way to large-scale quantum computing networks. Should the business world seize this opportunity, the synergy between classical telecommunications and quantum resources may become a key tool for the evolution of computing and information security.


 

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