Quantum breakthrough: Atoms connected to the Internet via fiber optics for the first time

Ytterbium-171 atoms once kept time in some of the world’s most precise optical clocks. Now, researchers at the University of Illinois have given them a new task, linking directly to photons at 1389 nanometers, a wavelength already optimized for fast, low-loss travel through standard telecommunication fibers.

The group also showed that the link works across many atom sites at once and still stays clean. In tests, photons crossed 131 feet of optical fiber while preserving the quantum signal needed for networking.

The project is led by Jacob P. Covey. His team is building a platform that treats widely used clock atoms as network connectors for long distance quantum links.

The team initially planned to use the green photon from the atom’s ground-state nuclear qubit but later discovered that the 1389-nanometer transition offered a far better path for creating stable, long-distance links.

Photons and fiber cables

Most atom-based systems give off visible or ultraviolet light, which doesn’t travel well through long fiber cables.

Standard communication fibers work best with light near 1550 nanometers, the range used by internet providers for sending data over long distances.

The Illinois device emits photons in the telecom fiber band from the start, so it avoids a separate converter that can waste photons and add unwanted noise.

That single choice can mean fewer errors when two remote labs try to share quantum information.

The team mapped a row of trapped atoms to a matching row of fiber cores. That geometry allowed many atom photon links to run at once without stepping on one another, and tests reported uniform fidelity across sites.

They verified that crosstalk stayed negligible while scaling the number of channels. The design is compatible with common fiber arrays already used in communication hardware.

Time bin encoding

The link stores information in time bin encoding, a method that represents a bit using two well separated arrival times.

It is robust in fiber because timing survives the small disturbances that can scramble polarization, and it is already common in quantum key distribution. as shown in recent encoding work.

In this experiment, the nuclear spin of a single atom became entangled with a photon that could arrive early or late. That pairing created a state that remains correlated even after traveling through the fiber.

Checking the correlations

After generating the atom photon pair, the photon entered a time delay interferometer that tests how the two time bins interfere. 

The researchers then detected photons using SNSPDs, superconducting nanowire single photon detectors, devices that catch single particles of light with very low false counts.

They reported an atom measurement corrected Bell state fidelity near 0.95 and identified photon detection errors as the main remaining limit. Those limits can be pushed lower with better filtering and calibration.

Networking can nudge nearby atoms and erase the state of a qubit that is supposed to be idle. The group built a protocol that protects a memory qubit, the qubit kept for storage, while communication qubits handle the network attempt.

They showed that the stored state stayed coherent during the send and detect cycle. That ability matters for any processor that must talk to the network without losing its place in a computation.

Photons, fiber, and distance

Telecom photons ride through miles of fiber cable with modest loss compared with visible light. That property keeps entanglement distribution practical over city scale distances without a repeater or a noisy frequency converter, a benefit supported by fiber standards.

Direct emission also simplifies the setup. Fewer optical components means fewer places to misalign and fewer failure modes in the lab.

The atom array was imaged onto a commercial fiber array, so alignment used off the shelf parts. That choice lowers the barrier for other labs that want to reproduce the platform and add more channels.

The team sent photons through a test spool of fiber that measured 131 feet and still recovered the expected interference pattern. That result is an early sign that modest lab distances will not be the bottleneck.

The measured fidelity was limited mostly by photon detection errors and imperfect interferometer stability. Those are technical issues more than fundamental barriers, and they usually improve with better calibration and temperature control.

The group outlined upgrades that target collection efficiency, timing stability, and detector performance. None require a different atom or a new protocol.

How they expect to speed things up

A key path is improving how many photons are collected from each atom. Placing the array in an optical cavity, a pair of mirrors that funnels light into a single mode, can increase the detected rate by orders of magnitude.

Higher rates mean faster attempts at making links, and that raises the chance of success for remote entanglement between two labs. Once two sites share an entangled pair, they can run protocols for secure keys or distributed sensing.

Fiber optics, photons, and the future

The same atom sits at the heart of some of the most accurate clocks ever built. Linking many of them could turn single clock labs into a synchronized network that averages noise and improves long term stability.

Quantum sensors benefit as well, because shared entanglement can boost precision beyond classical limits. The direct telecom link reduces friction in moving those ideas from theory into hardware.

This work shows that a single atomic species can carry both computing and networking roles. It also shows that careful engineering choices, not just new physics, decide whether a platform will scale.

The use of standard fibers and arrays is a practical signal to the field. It says that the physics is ready to meet the infrastructure.

The study is published in Nature Physics.

Image credit: Covey Lab.

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