Brookhaven and Stony Brook Just Linked a Quantum Network Through Open Air

In my last post, I laid out the fiber problem: quantum networks can't use classical repeaters because the no-cloning theorem forbids copying an unknown quantum state, so every photon has to survive, unassisted, from source to destination. Fiber compounds that: it loses about 0.2 dB/km, and its only efficient band (1550 nm) doesn't match the wavelengths most atomic memories emit, forcing lossy conversion steps at each end.

Commercial telecom has been married to one wavelength band for as long as I've been in the field, going back to writing the telecommunications curriculum for Verizon's NextStep program in 1995 and later directing NSF-funded Centers of Excellence in telecommunications and optics and photonics. My dad worked the generation before that, retiring in 1984 back when the network still ran on copper and fiber hadn't arrived yet. Brookhaven National Laboratory and Stony Brook University just did something a little different. 

Photons travel 13 miles through open air from Stony Brook's Quantum Watchtower to Brookhaven's Quantum Lighthouse, using adaptive optics instead of fiber. Link connects to existing 161 mile fiber network, with a 30 mile extension to Yale planned next.

On August 21, researchers sent single photons and entangled photon pairs 13 miles through open air, from Stony Brook's Quantum Watchtower to Brookhaven's Quantum Lighthouse in Upton, New York, no fiber involved for that leg of the trip. The daytime event was a formal demonstration for DOE and state officials. The actual first detection happened two days earlier, in the dark: at 12:26 a.m. on August 19, the Lighthouse recorded entangled photon pairs arriving from the Watchtower, confirmed through phase folded photon analysis comparing on-phase detection counts against background noise rates.

Both facilities exist to solve one problem: Brookhaven and Stony Brook need an unbroken line of sight to each other, which is why the Lighthouse sits on the only Brookhaven building with that sightline, a seven story rooftop installation, while the Watchtower sits atop Stony Brook's Health Sciences Center. Fog blocks the link outright. Bright daylight is a subtler problem. It raises atmospheric turbulence and buries the faint photon signal in background light, a limitation the Brookhaven team has compared to trying to spot a flashlight beam from a rooftop in broad daylight.

The optics came out of Brookhaven's Instrumentation Department, built on adaptive optics designs borrowed from the Vera C. Rubin Observatory. Photons leave the Watchtower through a fiber core five microns wide, about a tenth the width of a human hair. A telescope expands that pinprick of light into a 25 inch, 0.6 meter beam to match the primary mirror, while deformable mirrors correct for atmospheric turbulence in real time at kilohertz frequencies. At the Lighthouse, the process runs in reverse: the beam narrows back down and threads into a matching five micron fiber core for detection.

Commercial fiber networks are locked into wavelengths near 1550 nanometers because that band travels through glass with the least loss over distance. A free-space link carries no such requirement. Researchers can transmit infrared wavelengths native to the atomic systems and quantum processors themselves, opening a direct channel to entangle remote atomic memories without a wavelength conversion step.

The new link folds into an existing fiber network spanning 161 miles and eight nodes across Long Island and the New York City area, the longest metropolitan quantum network in the country. DOE Under Secretary for Science Dario Gil cut the ribbon on the receiving aperture at the August 21 event, framing the connection as a step toward linking individual quantum computers into something larger.

A third facility, functionally identical to the Lighthouse and Watchtower, is already built at Yale University in New Haven, Connecticut, with a 30 mile free-space link across Long Island Sound planned to connect Stony Brook and Yale directly. Past that, the team plans to repurpose the same rooftop telescope infrastructure to track low-earth-orbit satellites, laying groundwork for satellite-based quantum key distribution and a longer-term global quantum network. Funding comes from DOE's Office of Science, the National Science Foundation, and $300 million in New York Empire State Development money tied to Stony Brook's Quantum Innovation initiative.

This ties directly to Chapter 1 of Quantum from the Ground Up, which opens on the fiber problem: how to move quantum information over distance without destroying the fragile state that makes it quantum in the first place. Fiber solved part of that by forcing everything into a wavelength band it can carry efficiently. This link solves a different part by removing the requirement to force anything at all. This post will roll into the next quarterly edition of the book, out September 1. You can read the current edition here.

The Fiber Problem: Why Distance Breaks Quantum Networks

Every quantum network built so far runs into the same wall: how do you move a quantum state across distance without destroying the property that makes it quantum in the first place. That's the fiber problem. 

Diagram shows the photon's path: native wavelength out, up-converted into the fiber band, lossy fiber crossing, down-converted back, with the no-cloning constraint called out separately underneath since it's the reason none of that loss can be patched mid-flight.

Classical data degrades over distance too, but repeaters fix it. A signal gets weak, a repeater reads it, copies it, and sends a fresh copy further down the line. Quantum states can't do that. The no-cloning theorem, a hard result in quantum mechanics, says you cannot create an identical copy of an unknown quantum state. There's no way to read a photon's quantum state, copy it, and pass along a clean version. Doing so destroys the very state you were trying to preserve. Whatever leaves the source has to survive, unassisted, all the way to the destination.

Fiber makes survival harder the farther a photon travels. Standard telecom fiber loses roughly 0.2 decibels of signal per kilometer at the wavelength commercial networks use, a small number that compounds fast over distance. A classical signal can be boosted past that loss. A single photon carrying a quantum state can't be boosted, only lost. Every kilometer of fiber is another chance for that photon to get absorbed or scattered before it arrives.

There's a second problem. Commercial fiber carries light efficiently only in narrow bands, mainly around 1550 nanometers, because that's where glass loses the least light over distance. The atomic systems used to store and process quantum information, trapped ions, neutral atoms, certain solid-state qubits, usually don't emit or absorb light at 1550 nanometers. A photon leaving an atomic memory typically needs a wavelength conversion step just to enter the fiber network, and another one on the far end to be absorbed by the receiving memory. Each conversion is one more place to lose or degrade the state.

You can't clone a quantum state to fix loss along the way, and fiber adds distance-dependent loss plus a wavelength mismatch on top of photons that are already fragile.

In my next post I'll describe how Brookhaven National Labs and Stony Brook University have worked around the fiber "problem."

This is the problem Chapter 1 of Quantum from the Ground Up opens on. You can read the current edition of the book here.

Building Quantum Networks on Existing Fiber Infrastructure

Image AI Generated

I’ve written here about quantum networks and communications. These systems that connect quantum computers and devices using quantum entanglement hold enormous promise for secure communication and distributed computing. But getting them to work over real-world distances has proven challenging.

The problem comes down to wavelengths. Most quantum systems today use visible or ultraviolet light to create entanglement between atoms. But here's the catch: when you try to send these signals through fiber optic cables over long distances, they degrade rapidly. The sweet spot for fiber optics is the "telecom band" - wavelengths ranging from about 1,260 to 1,675 nanometers or nm (infrared light), with the most efficient transmission around 1,310 nm and 1,550 nm. At these wavelengths, signals can travel hundreds of kilometers with minimal loss.

Converting quantum signals from visible light to telecom wavelengths sounds like an easy fix, but it's not. The conversion process reduces efficiency and introduces errors that corrupt the delicate quantum states you're trying to preserve.

Researchers led by Prof. Jacob P. Covey at the University of Illinois have identified a solution described here: A new scalable approach to realize a quantum communication network based on ytterbium-171 atoms The solution uses ytterbium-171 atoms that naturally emit light at 1,389 nanometers—already in the telecom band. No conversion needed. It's like building a device that speaks the right language from the start.

Ytterbium-171 was chosen strategically. This isotope is already used in ultra-precise atomic clocks because it has an extremely stable internal state. The researchers realized they could exploit this stability for quantum networking while taking advantage of its telecom-compatible light emission.

What makes this work particularly significant is the team's approach to scaling. Instead of just connecting one atom at a time, they created an array of multiple ytterbium-171 atoms held in place by focused laser beams (called optical tweezers). They then aligned this array with standard fiber optic cables - similar to how you might plug multiple ethernet cables into a router. This parallelization means multiple quantum connections can be established simultaneously, like having multiple lanes on a highway instead of a single narrow road. The team demonstrated that all channels maintained high-quality entanglement with virtually no interference between neighboring connections - a critical requirement for practical networks.

The researchers used something called "time-bin encoding" to package their quantum information. Rather than encoding data in properties like light polarization (which can get scrambled in fiber), they encode it in the precise timing of when photons arrive. Think of it as Morse code at the quantum level - the message is in the timing pattern rather than the brightness or color.

One innovation that makes this practical is their "mid-circuit networking protocol." In quantum computing, one of the biggest challenges is that quantum states are fragile—they degrade quickly. This protocol allows the system to establish network connections while keeping other quantum data intact, like being able to download files on your computer without closing all your other programs.

The team demonstrated their system can:

·       Create high-quality entanglement between atoms and photons consistently across all channels

·       Maintain quantum connections after sending photons through 40 meters of fiber optic cable

·       Achieve entanglement fidelity approaching 99% with planned improvements

·       Operate multiple channels simultaneously without crosstalk

The researchers are already designing a second-generation system that will use optical cavities (essentially mirrors that bounce photons back and forth) to dramatically improve collection efficiency. This could increase networking rates by orders of magnitude.

The long-term vision is creating networks where quantum processors at different locations can share entanglement - enabling distributed quantum computing, synchronized arrays of atomic clocks for precision sensing, and fundamentally secure communication channels.

This work shows that quantum networks can be built using existing fiber optic infrastructure while maintaining the high fidelities needed for practical quantum applications. By combining telecom-compatible atoms with scalable parallel architecture, the team has created a roadmap for the quantum networks of the future.

The Birth of Modern Computer Communications: The Hayes Smartmodem

Another looking back post - it was 1982, and I was still trying to figure out what I wanted to do in life. At one time I thought I wanted to go to medical school but after working in a hospital microbiology lab, I realized that was not the path for me. Maybe I could do something in the communications field….

In the early 1980s, connecting computers over phone lines was a complex and frustrating process requiring specialized knowledge and equipment. That all changed in 1981 when Dennis Hayes and Dale Heatherington introduced the Hayes Smartmodem, a revolutionary device that would fundamentally transform how computers communicate. The Hayes Smartmodem 300 was the first modem to combine communication hardware with an intelligent microprocessor control system. Unlike previous modems that required manual configuration, the Smartmodem could be controlled through a standard command set—the now-famous "AT commands" (where AT stood for "Attention"). This innovation allowed software to directly control the modem, automating the complex process of establishing connections.

The AT Command Revolution

The AT command set, sometimes called the Hayes command set, revolutionized communications because it created a standardized way for computers to control modems through simple text commands.

 

Basic Structure and Function

AT commands follow a simple structure: they begin with "AT" followed by specific command
letters and parameters. For example:

·      ATD (Dial) - Instructs the modem to dial a number

·      ATH (Hang up) - Terminates the current connection

·      ATA (Answer) - Instructs the modem to answer an incoming call

·      ATZ (Reset) - Resets the modem to its default configuration

The genius of this system was its simplicity. Before Hayes, controlling modems required specialized hardware interfaces or complicated software. The AT command set turned modem control into simple text strings that any program could generate.

Historical Impact

When Dennis Hayes introduced this command set with the Smartmodem in 1981, he effectively created the first "smart" modem that could be programmed and controlled by software. This innovation:

• Allowed software to handle complex connection procedures automatically
• Enabled features like auto-dialing and auto-answering
• Created a standard that was widely adopted across the industry
• Made modems accessible to non-technical users

Legacy and Modern Applications

Remarkably, variants of the AT command set are still used today in many communication devices. Modern cellular modems, some smartphones, and IoT devices continue to use AT commands for configuration and control. For example, sending an SMS from some embedded systems still involves AT commands like AT+CMGS.

The AT command set represents one of those rare technological innovations that was so fundamentally sound that its basic principles have outlived the hardware for which it was originally designed. From controlling 300 bps modems in the early 1980s to configuring LTE and 5G modules today, the basic concept of "Attention + Command" has proven remarkably durable.

This standardization was perhaps the Hayes Smartmodem's most enduring contribution to computing history - creating a common language that allowed computers and communication devices to work together seamlessly, helping to build the connected world we know today.

Quantum Communications - Part 3: Photon Polarization and Superposition

 Building on Part 2’s discussion of polarization, let's look a little deeper at how light enables quantum communication. Superposition in quantum mechanics means a photon can exist in multiple polarization states at once, unlike classical objects that must be in one definite state. Looking at the diagram below, a photon isn't limited to being just vertical (1) or horizontal (0), but can exist in a mixture of both until measured. Think of it like a spinning coin - while spinning, it's neither heads nor tails but both possibilities at once. When we measure the photon's polarization (like catching the coin), it "collapses" into one definite state.

The diagram shows two measurement bases - rectilinear and diagonal. A photon in superposition measured in either base has a probability of being found in either state of that base. This property is crucial for quantum cryptography because any measurement by an eavesdropper forces the superposition to collapse, altering the photon's state and revealing the intrusion.

 

The 45° polarization state, shown in the diagonal base of our diagram, demonstrates one of the most fascinating aspects of quantum mechanics. While we might classically think of 45° as simply an angle halfway between horizontal and vertical, in quantum mechanics it represents something far more profound. When a photon is polarized at 45°, it literally exists in a perfect blend of horizontal and vertical states at the same time - not just leaning one way or the other, but fully in both states simultaneously.

 

This quantum behavior becomes clear when we measure these 45° polarized photons. If we measure using the rectilinear base (horizontal/vertical as shown in the left circle of our diagram), we get the following result: the photon will randomly show up as either horizontal or vertical with exactly equal probability. This isn't because we're measuring imprecisely or because the photon was "kind of" in both states - it was genuinely, mathematically, and physically in both states at once until the act of measurement forced it to pick one.

 

Think of it this way: if we send many 45° polarized photons through a horizontal polarizer, exactly half will pass through (registering as horizontal) and half will be blocked (registering as vertical). This isn't due to some classical "angled" behavior - it's a direct manifestation of quantum superposition, where the photon existed in both states simultaneously until we forced it to "decide" by measuring it.

 

This property is part of what makes quantum communication so secure: any attempt to measure these superposition states unavoidably disturbs them, making eavesdropping detectable.

Quantum Communications - Part 2: Polarization

In Part 1 of this series I discussed how quantum superposition allows particles to exist in multiple states at once until measured. This makes quantum information almost impossible to copy secretly, enabling ultra-secure communication systems that can detect eavesdropping attempts. Here we'll take a closer look at how this information is transmitted using light particles called photons. 

Light can be analyzed as either a ray or a wave, each model revealing different aspects of its behavior. The ray model treats light as straight lines traveling through space, useful for understanding reflection, refraction, and how lenses and mirrors work. The wave model shows light as oscillating electromagnetic waves, explaining phenomena like interference, diffraction, and polarization. While the ray model helps us design simple optical devices like eyeglasses, the wave model is necessary for understanding more complex effects like how polarizing filters work. Both models remain important in modern optics, with each being used depending on which aspects of light's behavior are most relevant to the situation at hand.

 

When it comes to polarization we need to think about light as a wave. Light waves oscillate perpendicular to their direction of travel, Unpolarized light ( like we get from natural sources like the sun or artificial sources like light bulbs) vibrates in all possible directions like a rope being waved up-down, side-to-side, and at every angle in between. A polarization filter works like a microscopic venetian blind with extremely fine parallel slits. When light encounters the filter, only the waves that vibrate parallel to these slits can pass through completely. Waves vibrating in other directions are either blocked entirely or have only their parallel components transmitted. The light that emerges from the filter is polarized, meaning all the waves are vibrating in the same direction. 

Here's a quick 3 second video I made demonstrating light passing through a polarizing filter.

Before the filter: 

• Horizontal component (blue wave)
• Vertical component (pink wave)
• 45-degree component (green wave, thicker line) All components are present in the unpolarized light

The Filter: 

• Oriented at 45 degrees
• Only allows waves aligned with its transmission axis

After the filter: 

• Only the 45-degree component (green wave) passes through
• Horizontal and vertical components are blocked
• The transmitted light is polarized along the 45-degree axis

Notice:

• Only transmits light waves that oscillate parallel to its transmission axis (45 degrees in this case)
• Waves at other angles are either blocked or have only their 45-degree component transmitted
• The result is polarized light oscillating only at 45 degrees

This selective transmission property makes polarizing filters particularly useful in everyday applications. For example, polarizing sunglasses can effectively reduce glare because light reflecting off horizontal surfaces like water or roads tends to become partially polarized in the horizontal direction. The sunglasses, which have vertical polarizing slits, block this horizontal glare while still allowing other light through. A demonstration of how polarization works involves using two polarizing filters. When light passes through the first filter, it becomes polarized in one direction. If you then rotate a second filter 90 degrees relative to the first, no light gets through at all because the polarized light from the first filter is now perpendicular to the slits in the second filter.

 

So what does polarization have to do with quantum communications? In quantum communications individual photons can be prepared in specific polarization states (vertical, horizontal, or diagonal) to represent quantum bits. Due to quantum mechanics principles, any attempt to measure these polarization states disturbs them, making secure communication possible - eavesdropping can be detected. Polarization also enables quantum entanglement, where measuring one photon's polarization instantly determines its entangled partner's state, even at a distance.

 

While powerful, polarization methods face practical challenges as polarization states can degrade during transmission through optical fibers or atmosphere, requiring sophisticated error correction methods. For these reasons, quantum communications can use several alternatives to polarization for encoding quantum information. Time-bin encoding uses photon arrival times and works well in fiber optics where polarization degrades. Phase encoding utilizes phase differences between photon paths, while frequency encoding uses different photon frequencies. Orbital Angular Momentum (OAM) encoding exploits spiral patterns of light waves, potentially carrying more information than polarization. Path encoding, which uses different physical routes for photons, is useful in integrated photonic circuits. Each of these methods has its own advantages and the choice often depends on the specific application and transmission medium being used. For instance, time-bin encoding tends to be more robust for long-distance fiber communication, while OAM can potentially carry more information per photon. 

Quantum Communications – Part 1

 Computers, communications, photonics, cybersecurity…… some of my favorite technologies all bundled together in quantum communications! But… what is it? How does it work? Let's take an introductory look.

In quantum mechanics, something called superposition allows systems to exist in multiple states simultaneously - like a spinning coin being both heads and tails at once, until observed. Only measurement forces it into a definite state. This principle affects quantum information through the no-cloning theorem, which states that it's impossible to create an exact copy of an unknown quantum state due to quantum mechanics' mathematical foundations. This feature enables quantum key distribution (QKD), which creates unbreakable encryption keys. Any eavesdropping attempt disturbs the quantum states due to the no-cloning theorem, instantly revealing the intrusion. While classical information can be copied perfectly, quantum information's resistance to copying both protects it and makes quantum teleportation the only way to transfer quantum states.

 

How about an example? Let’s now compare sending a classical letter and sending a quantum letter using two diagrams I’ve created. These diagrams split into two parallel workflows showing classical versus quantum communication highlight the key security advantages of quantum communication over classical methods.

 

The classical letter path shows a letter that can be intercepted, read, and copied without detection as it moves from sender to recipient through the postal system.

The quantum letter path illustrates how quantum letters behave differently:

• The letter exists in superposition (blue state) until measured
• Any attempt to read/copy disturbs the quantum state (changes to red)
• This disturbance is detectable when received by the recipient, revealing tampering

We’ll dig a little deeper in future posts – for now think of quantum communication as the first step toward a quantum internet - one that operates on the powerful principles of quantum physics rather than classical physics. While we may not see quantum email on our phones anytime soon, the technology is steadily advancing from science fiction toward practical reality.

Closing the loop with IP/Optical Integration

I've spent the last 17 years focused on Internet Protocol (IP) over various transport systems - wired (copper), wireless and optical. With the explosion of video, social media and other bandwidth hungry applications we've seen fiber moving closer and closer to the end user. Wireless is the perfect example with towers back-hauled into the network by fiber. It's really just the last mile/final connection that is typically not optical fiber based for most of us.

We're seeing IP/optical integration today really ramping with these things called software defined networks (SDNs). I wrote a post defining and describing SDN's last month titled SDN: When The Hardware Becomes A Little More Soft

With the move to all-IP, SDN and cloud services, many service providers are now integrating IP routing and transport. In this short 4 minute and 50 audio clip, Arnold Jansen discusses how IP/optical control integration can help operators simplify and streamline their operations and drive better cost synergies.



 Smart, fast, efficient. Good stuff.

Verizon Trimming Some Wireline Limbs

I've been teaching Verizon technicians in a program called NextStep since the mid 1990's. The Next Step Program allows contract qualified Verizon associates who are members of the Communications Workers of America (CWA) or the International Brotherhood of Electrical Workers (IBEW) to earn an Associate in Applied Science degree in Telecommunications Technology from a participating college. It's been a great opportunity for everyone involved to keep up and learn as the industry has transitioned.

This morning I taught my first class of the fall semester and we had some interesting discussion on where copper based landline services like DSL are going. The other night on Jim Cramer's show, Verizon CEO Lowell McAdam opened up a bit on the companies plans. Here's some back and forth from the show posted at  Stop the Cap!:

Jm Cramer, CNBC: “[Under former Verizon CEO Ivan Seidenberg, Verizon] took areas that really weren’t growth areas and sold them to Frontier and other players. Would you be able to get rid of some of your underperforming landline businesses to be able to increase [Verizon's] growth even further?”

Lowell McAdam, Verizon: “That is a possibility. [...] If you talk about opportunities here, now that we have One Verizon, [...] we are going to trim some limbs around the tree here. Things that aren’t performing will not be a part of our portfolio so we can invest in things that will drive the kind of growth we are excited to be able to tap here.”

In New Jersey and New York, Verizon is moving on a wireless landline replacement called Voice Link. It's optional for some customers but many are thinking it will replace copper services in there is approval from the states regulators. Verizon is calling Voice Link an improvement for voice customers dealing with repeated service calls.

Bloomberg estimates the Verizon wireless net worth is around $289 billion while Verizon wireline (landlines, FiOS and business broadband) is worth just $24 billion. Looking at revenue, Bloomberg says Verizon wireline totaled $39.8 billion last year which is down from $50.3 billion in 2007. During the same period, Verizon wireless revenue was up 73% to $75.9 billion.

It's pretty clear where this is all going - at least when it comes to Verizon wireline.

You can read a transcript of the complete McAdam interview linked here.

Watching What You Do While You Watch TV

Verizon recently filed a patent application that would target television ads using real time information collected by infrared cameras and microphones in you DVR. This is wild stuff - here's some examples of how this system would work right out of the filed document:

• if detection facility 104 determines that a user is exercising (e.g., running on a treadmill, doing aerobics, lifting weights, etc.), advertising facility 106 may select an advertisement associated with exercise in general, a specific exercise being performed by the user, and/or any other advertisement (e.g., an advertisement for health food) that may be intended for people who exercise. 

• if detection facility 104 detects that a user is playing with a dog, advertising facility 106 may select an advertisement associated with dogs (e.g., a dog food commercial, a flea treatment commercial, etc.). 

• if detection facility 104 detects one or more words spoken by a user (e.g., while talking to another user within the same room or on the telephone), advertising facility 106 may utilize the one or more words spoken by the user to search for and/or select an advertisement associated with the one or more words. 

• if detection facility 104 detects that a couple is arguing/fighting with each other, advertising facility 106 may select an advertisement associated marriage/relationship counseling. 

• if detection facility 104 detects a particular object (e.g., a Budweiser can) within a user's surroundings, advertising facility 106 may select an advertisement associated with the detected object (e.g., a Budweiser commercial). 

•  if detection facility 104 detects a mood of a user (e.g., that the user is stressed), advertising facility 106 may select an advertisement associated with the detected mood (e.g., a commercial for a stress-relief product such as aromatherapy candles, a vacation resort, etc.).

The image posted is also from the patent application and shows the detection zone. 

Pets, people, conversations, moods, beer cans?? I don't think this is something I'd want in my home.

Data Transmission on T1 Carriers - Part 2

In Part 1of this topic I described how a T1 carrier is used to transmit data. Data transmission by nature is "bursty" meaning large amounts of information are typically transmitted and then followed by relatively quiet transmission periods. This can cause transmission problems for T-carrier systems since they rely on timing synchronization. Let's take a look how this potential problem is avoided.