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University of California, Santa Barbara (UCSB) quantum information science researchers found a new, highly robust silicon qubit that could form the basis of scalable quantum technology. The hydrogen-free CN center solves silicon-based quantum emitter manufacturing problems.

The team, led by Materials Professor Chris Van de Walle, has found a stable defect that is compatible with industrial processes, suggesting a way to link laboratory quantum research with large-scale semiconductor-based quantum device manufacturing.

The Silicon Advantage

For the perfect qubit, the quantum equivalent of a classical computer bit, materials that are easy to create in vast quantities have been sought. Silicon, the core of the trillion-dollar semiconductor industry, is best for this transformation. Because silicon chip production infrastructure exists, researchers can employ this material without adopting new manufacturing paradigms.

Quantum technologies require “fab-friendly” physical systems with desirable quantum characteristics. Researchers have struggled to find silicon faults that are physically durable and can communicate across long distances using present infrastructure. CN center discovery solves communication and stability difficulties.

T Center “Hydrogen Fragility” Resolved

Before the CN center was discovered, the T center dominated scientific interest. The T center, a silicon imperfection consisting of carbon and hydrogen atoms, can store quantum information for long periods of time, like diamonds' NV center.

But hydrogen is the T center's "Achilles' heel". In a crystal lattice, hydrogen atoms are notoriously unstable because they are “slippery” and migrate easily during high-temperature heating and chemical processing for chip production. This sensitivity makes it difficult for engineers to create millions of identical T centers on a silicon wafer, which is needed for scalable quantum processors.

CN Center: Strong Alternative

To address this dependability issue, the UCSB Computational Materials Group used powerful first-principles computer simulations to find a hydrogen-free replacement. Their analysis revealed the CN center, a one-carbon (C)-one-nitrogen (N) compound.

The CN core is stronger than the hydrogen center because carbon and nitrogen produce stronger and more stable silicon lattice connections. While overseeing the experiment, UCSB postdoctoral scholar Kevin Nangoi noted, “This defect will be more robust and easier to realize in actual devices because it does not contain hydrogen like the T center does.”

The simulation findings reveal that the CN center duplicates the T center's electrical and optical features without fabrication concerns. According to project postdoctoral researcher Mark Turiansky, the core is solid and stays stable even under rigorous heat processing conditions used in conventional semiconductor manufacturing.

Transitioning to the Quantum Internet

The CN center is stable and communicatively gifted. For a global “Quantum Internet” to exist, qubits must produce light in the telecom band, which may pass via fiber-optic cables with little signal loss.

These telecom photons are naturally emitted by the CN center. A stable “spin” that serves as quantum memory can be directly coupled to a quantum communication unit, a “photon,” by building a spin-photon interface. Due to its compatibility with global fiber-optic networks, the CN center is a strong candidate for long-distance quantum networking.

Simulation of Future Hardware

First-principles computer simulations enabled this discovery. These advanced models allow researchers to predict the properties of material systems that have not yet been developed in a lab. Theoretical models guide technical efforts to create novel quantum devices, saving time and money.

Professor Van de Walle noted that if the CN center is experimentally proven, it might be used as a building block for electronics that use the same silicon material as modern computers and cellphones.

Moving Forward: Experimental Validation

This research will proceed to experimental validation. To study the CN core physically, scientists worldwide will “plant” carbon and nitrogen atoms into silicon lattices.

The CN center may become the industry standard for future quantum hardware if experiments match UCSB calculations. This suggests that a fault-tolerant quantum computer that can simulate new drugs or crack complex encryptions may require a precise silicon technology enhancement rather than a manufacturing revolution.

Microwave Quantum Networks

A microwave quantum network that functions resiliently at 4 Kelvin (K) temperatures has been shown, transforming the quantum internet. Researchers Qiu and colleagues challenged the scientific assumption that quantum communications are too delicate to survive outside ultracold conditions with this breakthrough. This breakthrough overcomes “thermal noise” that destroys quantum information, enabling scalable, more accessible quantum computing designs.

The Thermal Noise Challenge

Quantum communication can be used for secure data transport and distributed computing. Communication is usually done with superconducting circuits and microwave photons. These photons, however, are infamously sensitive to their surroundings. Even a small amount of heat causes “thermal noise” that swiftly tears down fragile quantum states in a normal environment.

Due to this issue, quantum networks have had to operate in dilution freezers' “deep freeze” (approximately 10 millikelvin). Due to little thermal occupation of communication channels, heat-induced noise does not “smother” quantum signals at these temperatures. The complexity, energy consumption, and cost of maintaining such severe temperatures hinder quantum technology mass deployment.

A New Material Basis

Innovative material science and a new cooling mechanism are behind the breakthrough. The group used a NbTi superconducting transmission line. Niobium–titanium superconducts at 4 K, but aluminum requires much lower temperatures. This material communicated with low loss and great fidelity above millikelvin.

Working at 4 K may allow the system to integrate with more widely used cryogenic infrastructures, reducing the complexity and cost of prior systems' ultra-low temperature needs.

Radiative cooling: trickling heat away

The study's biggest breakthrough was “radiative cooling”. The transmission line is thermalized at 4 K, but the researchers reduced the channel's "effective" thermal noise to levels much lower than the surrounding environment.

The process involves overcoupling the microwave communication channel to a 10-millikelvin "cold load". Rapid thermal photon dissipation into the load is achieved by aggressively connecting the 4 K channel to this much colder reservoir. This results in a very low effective thermal photon number of 0.06, two orders of magnitude lower than the noise levels projected at 4 K. Despite its warmer environment, the channel behaves like it's at deep cryogenic temperatures.

Dynamic Handshake

The group developed a dynamic channel adjustment method for actual communication. First, the transmission line is attached to the cold load to cool. After suppressing noise, the system decouples the load virtually instantly with a quantum state transfer.

The channel "rethermalizes" (warms up) as soon as it is decoupled, but the researchers showed that state transmission is fast enough to overcome thermal interference and sustain quantum coherence throughout the operational window.

Outperforming Classics

Experiments validated the network's quantum capabilities. Without readout error correction, the team achieved 58.5% process fidelity for direct quantum state transfer between two superconducting qubits. They also identified 52.3% Bell state entanglement fidelity. Importantly, both figures above the 50% "classical threshold," proving that the network can sustain quantum advantages in a noisy microwave environment.

The researchers constructed a 1 Kelvin setup to test the limits farther. This setup improved coherence times, providing 93.6% Bell entanglement fidelity. This unprecedented level of precision for a thermally robust network is needed to develop fault-tolerant protocols for large-scale systems.

Proving Quantum Reality

An important milestone was the experiment's clear breach of Bell's inequality. This was done via remote entanglement without reading error correction. The violation of Bell's inequality is the “gold standard” for proving that the correlations are quantum and nonlocal. The network works beyond classical restrictions in high-temperature conditions, as shown by this verification.

Path to Quantum Internet

This discovery changes how researchers approach ambient noise's "bottleneck". The work showed that cool reservoirs and coupling strength engineering may suppress heat, enabling distributed quantum computing. The robust channels connecting modular quantum nodes in this future design may be less susceptible to their environment than imagined.

Rare-Earth Crystal Advancements Allow a Quantum Internet Compatible with Telecom Service

Telecom-Friendly Quantum Nodes

A multinational team of scientists created telecom-compatible quantum nodes using a dual-species rare-earth crystal, advancing global quantum communications. This research discusses how doping erbium ions into a europium-based host could improve optical interface and quantum storage.

The initiative involved the International Quantum Academy, Australian National University, and Shenzhen SUSTech experts. Quantum networking requires quantum repeaters that can store data for a long period and work with regular telecommunications infrastructure. Their research addresses this.

Quantum Gap Filling

A quantum internet uses quantum repeaters as relay stations to extend quantum messages over long fiber-optic cable distances. These repeaters require a platform to transmit and store quantum states with telecom wavelength photons.

The team employs erbium-doped stoichiometric EuCl3 ⋅ 6H2O crystals. Both rare-earth elements serve complimentary roles in this “dual-species” system. The scientific community knows europium's (Eu3+) extraordinary coherence, which is essential for long-term quantum storage. Erbium (Er3+) is ideal for optical interfacing with standard fiber networks due to its direct telecom-band emission and microwave compatibility.

“Frozen Core” Innovation

The study's discovery of a “frozen core” influence is surprising. The researchers used the spins of the erbium ions to shield the quantum states of the europium ions by cooling the crystal to 60 mK and applying a modest magnetic field of 0.1 T.

This raised Eu3+ optical coherence time from 62 to 162 microseconds, which the authors say is approaching the theoretical lifespan limit. This interaction enabled hour-long hyperfine state lifetimes, which are necessary for ultra-long-term quantum storage and may help satisfy the 10-hour criteria proposed in related high-performance research.

The researchers also measured the intensity of Er3+ and Eu3+ ion contact, which ranged from tens to hundreds of kilohertz. This interaction shifts the optical transition frequencies of europium ions, creating “satellite lines” in the absorption profile for accurate quantum control.

A Global Future Technology Collaboration

The team developed the project concept with F. Wang, R. Ahlefeldt, M. Sellars, and M. Zhong. At SUSTech, Mucheng Guo and Wanting Xiao spearheaded the experimental effort, while numerous Shenzhen and Canberra team members did theoretical modeling and analysis.

This project received financing from the National Natural Science Foundation of China and the National Science and Technology Primary Project of China. This investment shows the strategic importance of rare-earth materials in photonic quantum technology development.

Toward Quantum Network

The consequences of this work reach beyond the lab. The team has proven that combining the stabilizing and linking features of erbium and europium may develop a promising quantum node material.

Rare-earth-doped antiferromagnets and single erbium ions in solids have been studied, but the dual-species stoichiometric crystal can be used in telecom-compatible architectures. As safe, fast quantum communication becomes more important, these crystals could form a global quantum internet.

Researchers demonstrated a single-photon edge in quantum cryptography by developing a robust quantum coin flipping protocol using a deterministic quantum dot light source. Quantum key distribution typically targets trusted partners, while this experiment addresses insecure participants.

Instead of laser pulses, the team used on-demand single photons, which improved performance and minimized cheating. A combination of high-efficiency detectors and advanced polarization-state encoding ensured security across lossy channels. This milestone implies that a quantum internet will require sub-Poissonian light to build complex cryptography primitives. These findings show that high-performance quantum sources improve secure communication beyond key exchange.

Researchers Get “Coin Flipping” Idea for Quantum Web

Researchers have advanced quantum cryptography beyond "secret key" sharing, paving the way for a physically secure global communication network. A team from the Technical University of Berlin, the Chinese Academy of Sciences, and the University of Münster implemented a secure “quantum coin flipping” protocol using individual light particles, proving that quantum physics can protect users even when they don't trust each other.

Quantum Key Distribution (QKD) has been the gold standard in quantum security for decades since it lets two friends construct a secret key in perfect secrecy. QKD is limited, according to academics, because it assumes confidence. From digital voting and online casinos to complex corporate contracts, strangers or rivals with every motivation to cheat often communicate.

The “Distrustful” Setting Challenge

Manuel Blum coined “coin flipping by telephone” in 1983. Simple: a coin toss between two distant people should be fair so neither can affect the outcome. In the future, powerful computers could solve this complex classical mathematics.

In place of mathematical complexity, quantum mechanics uses natural principles to answer. Initial laser pulse research had basic limitations. A clever cheater could “peek” at the coin before it lands by intercepting one photon while letting others through since lasers create “faint pulses” that sometimes comprise many photons.

Deterministic Solution

Berlin's team used a silicon quantum dot-based deterministic single-photon generator to circumvent this. This “artificial atom” can release one photon at a time, unlike a probabilistic laser. The researchers' "purcell enhancement," which involved inserting this quantum dot inside a micro-cavity, dramatically enhanced the source's speed and efficiency. “Our work represents a significant step towards the implementation of complex cryptographic tasks in a future quantum internet by demonstrating a single-photon quantum advantage in a cryptographic primitive beyond QKD,” the researchers stated.

Trial: Bob vs. Alice

Alice, one of the experimenters, generates 50,000 pulses with one photon encoded with a certain polarization. These states are slightly skewed to maximize security compared to regular quantum bits. Bob receives them from Alice and randomly measures them.

Bob is prevented from cheating by several protocol checks. Bob must reveal which photon he first spotted without knowing its condition. After that, Alice gives over the photon "key". As Bob's measurement deviates from Alice's original condition, the protocol stops the cheating attempt.

One of the project's greatest technological successes was a 2.8% Quantum Bit Error Ratio (QBER). This accuracy was needed because quantum coin flipping is more error-prone than standard QKD. The scientists used advanced “Manchester coding” to triple the internal clock rate to 160 MHz to minimize electrical drifts, which commonly cause errors in random sequences.

Real-World Results

Researchers securely flipped about 1,500 coins each second. The system's performance over simulated fiber-optic distances was assessed. At 3 dB signal loss, the "quantum advantage," the advantage quantum physics has over the greatest classical cheating approach, persisted, but noise eliminated it at 6 dB.

Most crucially, the experiment showed that single photons outperform laser bursts. Laser intensity can be reduced to a very low level, but coin flipping would be quite slow. Single-photon sources offer better performance and “reduced bias”.

Future: Casinos to Clouds

This work affects the Future Quantum Internet architecture. These single-photon sources could provide “commitment schemes” for digital auctions, “leader election” in decentralized networks, and fair online games in addition to coin flips.

The team is preparing for future milestones. Using “telecom wavelength” photons, scientists want to improve communication range to tens of kilometers. By increasing the clock rate to the GHz region, which is attainable with their quantum dot, they anticipate they may reach 24,000 secure coin flips per second.

Qunnect Inc.

Montana State University (MSU) launched the Northwest's first quantum entanglement network with Qunnect's Carina product suite. The university becomes a national quantum innovation leader with high-performance entanglement distribution on campus-scale telecommunications fiber.

New Quantum Research Era in Montana

The implementation is crucial to Montana State University's Applied Quantum CORE program, QCORE. This project promotes quantum science through top-tier research, training, and strategic connections. By adding the Carina suite, MSU is establishing a campus that integrates quantum computers and cutting-edge sensor technology.

This network will allow researchers to demonstrate theoretical models and execute actual demonstrations as a “powerful testbed.” Focus areas for this infrastructure include:

Secure quantum communication

Quantum distributed computing

Quantum-capable sensors

Scalable quantum network

Tech Breakthroughs: Carina Advantage

The Carina product suite is unique because it incorporates numerous complex quantum networking components into a rack-mount unit for traditional telecommunications fiber. Unlike many laboratory settings that require certain circumstances, Carina is designed for real-world deployment.

Atom-based entangled-photon generators produce high-rate photon pairs with sub-GHz linewidth, making them more efficient than crystal-based methods for many research purposes.

Over fiber distances up to 100 km, adaptive polarization correction maintains entanglement integrity even in changing environmental circumstances.

Module integration: The system operates with both traditional data channels and current DWDM networks, making it a “turnkey solution” for fiber-based entanglement dissemination.

Global Context and Success

One of the few colleges using Qunnect's technology is MSU. In the GothamQ project in New York City, the Carina rack set commercial-grade fiber performance records. The technology has also helped Deutsche Telekom's Berlin project BearlinQ achieve record entanglement dispersion distances since 2024.

Qunnect CEO Noel Goddard says MSU has been experimenting with entanglement for over a year. This latest deployment is the “next step in moving practical quantum networks out of the lab and into real-world research deployments”.

Generational Empowerment

The network's technical achievements and instructional value are important. Prof. Krishna Rupavatharam, CTO of QCORE, calls photonic quantum networking experience a “major accelerator” for students. This infrastructure lets researchers and students immediately examine and build on quantum networks to prepare them for the rapidly increasing quantum sector.

QCORE received a $31.5 million contract from the Air Force Research Laboratory (AFRL) to expand its research and test beds, demonstrating its speed. MSU teamed with Rigetti Computing to further quantum research.

Economic and Scientific Impact

This network is expected to boost Montana's economy by attracting top scientists, research grants, and high-tech partnerships. By building the infrastructure for the “next era of quantum science,” MSU can lead the quantum internet.

Quantum computing is rapidly moving from theoretical study to large-scale application, and silicon photonics is the fundamental technology to overcome scaling limits. Traditional quantum systems use superconducting circuits and other matter-based qubits, but manufacturers are increasingly using photons to bridge the gap between small-scale prototypes and commercially viable million-qubit computers.

Upcoming Architecture Standard

Silicon photonics integrates light-based components directly onto silicon chips using tiny optical circuits to guide and control photons instead of electrical signals. This modification is notable because photons resist external noise, a quantum electronics issue that causes decoherence. Researchers can use light to transfer quantum states with high fidelity and little interference to sustain entanglement for complex calculations.

Photonic systems lose less energy than copper-based electronics, which have high resistive losses and heat. Silicon photonics is well-established in data centers and telecommunications, and its efficiency is being used to design quantum processors.

Solution for Scaling

One of the biggest challenges in quantum computing is scaling systems to thousands or millions of qubits. Traditional matter-based systems require complex, extensive wiring that is hard to expand. However, silicon photonics creates dense, low-loss interconnects using optical waveguides. These waveguides create “quantum interconnects” for scalable, modular designs by connecting many qubits across numerous chips.

The technology also uses CMOS manufacturing infrastructure. Photonic quantum devices can be mass-produced utilizing semiconductor fabrication methods due to their compatibility, reducing production hurdles and easing lab-to-manufacturing transition.

More efficient: Light vs. Electrons

Light-based electronics have many technical benefits over copper-based ones. Industry data shows that photonics can propagate signals faster and have a wider bandwidth (Terahertz vs. Gigahertz for electronics).

As “flying qubits,” photons enable safe quantum communication over longer distances. This may be the most important development for the future “quantum internet”. Silicon devices for quantum key distribution (QKD) are being developed to build a safe and useful quantum network.

Comparing the two platforms shows why the industry changed:

Energy Efficiency: Photonics has no resistive heating and low loss, unlike electronics.

For many matter-based qubits, substantial cryogenic cooling is needed. However, many photonic devices may operate at ambient temperature or close to it, reducing hybrid design cooling costs.

Scalability: Wavelength-division multiplexing can parallelize photonics, but heat dissipation and crosstalk limit electrons.

Global Impulse and Utility-Scale Goals

A global race for quantum dominance has begun. Researchers and nations are introducing photonic quantum processors that can speed up tough tasks thousands of times. Businesses of all sizes are investing heavily in these platforms to build error-resistant machines.

Many businesses aim for the million-qubit “utility-scale” quantum computing computer. By replacing cryogenic structures with photonic designs, these massive devices may fit into data centers. This would boost their industrial usage in cryptography, AI, and drug development.

Technical Challenges Ahead

Despite the excitement, silicon photonics must overcome various technological challenges before becoming the industry norm. Producing identical, on-demand single photons at scale is difficult for researchers. While integrating electronics and optics on a chip has benefits, it also creates fabrication and heat management challenges.

Quantum error correction in photonic systems remains resource-intensive. Industry consensus is that silicon photonics is the most promising quantum computing technology due to its energy efficiency, scalability, and manufacturing compatibility.

Overview

This article explains the invention of highly effective integrated quantum memory, a quantum computing hardware breakthrough. Researchers employed rare-earth-ion-doped crystals to achieve record-breaking energy storage efficiencies of over 80% in these devices. The scientists employed laser-fabricated waveguides and ultra-thin membranes to construct compact, scalable devices.

Due to their multimodal capability, these new designs can store multiple data points across many temporal modalities. Technology like spectral tunability lets hardware be adjusted to fit network needs. These advances provide a solid foundation for complicated photonic computers and large-scale quantum repeaters.

Integrating Quantum Memory Breaks Efficiency Records

Researchers at the University of Science and Technology of China (USTC) have developed integrated quantum memory with unparalleled efficiency, advancing the global "quantum internet." Rare-earth-ion-doped crystals and sophisticated microcavity designs helped the team overcome a 50% efficiency threshold that has prevented scalable quantum networks.

Quantum “Hard Drive” discovery

As computers need RAM and hard drives to store data, quantum networks need a way to store and retrieve quantum states of light. Photonic processors, which may power future quantum computers, and quantum repeaters, which extend quantum communication, use these “quantum memories”.

However, creating efficient, integrated memory that fit on a chip has been difficult. Although larger systems using massive gas clouds have achieved great efficiencies, integrated solid-state systems have not exceeded 27.8%. The researchers wrote that efficiency is the most essential factor of merit and that enhancing efficiency is necessary to increase entanglement distribution rates and quantum gate operating performance. To use error correction and function under the no-cloning regime, 50% efficiency is a “pivotal threshold”.

Two-Prone Structure

The USTC team, led by Professor Zong-Quan Zhou and colleagues, made this finding using two innovative designs based on europium-doped crystals (151Eu3+:Y2​SiO5). Long-term light storage makes these crystals valuable, yet they have low optical absorption.

To overcome the issue, the scientists used impedance-matched microcavities, which use mirrors to “trap” light and strengthen its interaction with the crystal.

The Waveguide Cavity (WGC) uses a laser-written optical waveguide in a bulk crystal. The highest solid-state photonic storage efficiency for weak coherent pulses was 80.3%.

FBC is an idea that uses a fiber mirror with ultra-thin crystal membranes (200 micrometers) to create a microcavity. Real “single photons” signaled at telecom wavelengths were 69.8% efficient.

Tunability and Multitasking Beyond Speed

The innovation includes efficiency, adaptability, and capacity. Quantum internets must handle lots of data at once. USTC devices may store up to 20 temporal modes with an average effectiveness of 50%.

The thin-membrane FBC architecture allows spectrum tunability, the researchers observed. They physically strained the membrane to adjust the memory's frequency within 10 GHz. This allows quantum networks to have flexible interfaces, researchers claimed. The memory can “talk” to numerous quantum light sources with slightly different frequencies due to its tunability.

Technology Cuts

Miniaturization may be the greatest achievement. Working together, the group reduced device volume to 4x10−5 mm3. Compared to other effective quantum memories, this is almost three orders of magnitude smaller.

The extraordinary compactness and 3D femtosecond laser micromachining of waveguides enable high-density spatial multiplexing. Packing thousands of these microscopic memory units onto a chip might produce powerful quantum processors.

Future of Quantum Internet

Even with unparalleled results, the team is preparing ahead. If internal losses are eliminated, efficiency may exceed 90%. Furthermore, they are creating "fiber pig-tailing," packing devices to link to existing fiber-optic networks.