A new, tunable smart surface can transform a single pulse of light into multiple beams, each aimed in different directions. The proof-of-principle development opens the door to a range of innovations in communications, imaging, sensing, and medicine.

The research comes out of the Caltech lab of Harry Atwater, a professor of applied physics and materials science, and is possible due to a type of nano-engineered material called a metasurface. “These are artificially designed surfaces which basically consist of nanostructured patterns,” says Prachi Thureja, a graduate student in Atwater’s group. “So it’s an array of nanostructures, and each nanostructure essentially allows us to locally control the properties of light.”

The surface can be reconfigured up to millions of times per second to change how it is locally controlling light. That’s rapid enough to manipulate and redirect light for applications in optical data transmission such as optical space communications and Li-Fi, as well as lidar.

“[The metasurface] brings unprecedented freedom in controlling light,” says Alex M.H. Wong, an associate professor of electrical engineering at the City University of Hong Kong. “The ability to do this means one can migrate existing wireless technologies into the optical regime. Li-Fi and LIDAR serve as prime examples.”

Metasurfaces remove the need for lenses and mirrors

Manipulating and redirecting beams of light typically involves a range of conventional lenses and mirrors. These lenses and mirrors might be microscopic in size, but they’re still using optical properties of materials like Snell’s Law, which describes the progress of a wavefront through different materials and how that wavefront is redirected—or refracted—according to the properties of the material itself.

By contrast, the new work offers the prospect of electrically manipulating a material’s optical properties via a semiconducting material. Combined with nano-scaled mirror elements, the flat, microscopic devices can be made to behave like a lens, without requiring lengths of curved or bent glass. And the new metasurface’s optical properties can be switched millions of times per second using electrical signals.

“The difference with our device is by applying different voltages across the device, we can change the profile of light coming off of the mirror, even though physically it’s not moving,” says paper co-author Jared Sisler—also a graduate student in Atwater’s group. “And then we can steer the light like it’s an electrically reprogrammable mirror.”

The device itself, a chip that measures 120 micrometers on each side, achieves its light-manipulating capabilities with an embedded surface of tiny gold antennas in a semiconductor layer of indium tin oxide. Manipulating the voltages across the semiconductor alters the material’s capacity to bend light—also known as its index of refraction. Between the reflection of the gold mirror elements and the tunable refractive capacity of the semiconductor, a lot of rapidly-tunable light manipulation becomes possible.

“I think the whole idea of using a solid-state metasurface or optical device to steer light in space and also use that for encoding information—I mean, there’s nothing like that that exists right now,” Sisler says. “So I mean, technically, you can send more information if you can achieve higher modulation rates. But since it’s kind of a new domain, the performance of our device is more just to show the principle.”

Metasurfaces open up plenty of new possibilities

The principle, says Wong, suggests a wide array of future technologies on the back of what he says are likely near-term metasurface developments and discoveries.

“The metasurface [can] be flat, ultrathin, and lightweight while it attains the functions normally achieved by a series of carefully curved lenses,” Wong says. “Scientists are currently still unlocking the vast possibilities the metasurface has available to us.

“With improvements in nanofabrication, elements with small feature sizes much smaller than the wavelength are now reliably fabricable,” Wong continues. “Many functionalities of the metasurface are being routinely demonstrated, benefiting not just communication but also imaging, sensing, and medicine, among other fields... I know that in addition to interest from academia, various players from industry are also deeply interested and making sizable investments in pushing this technology toward commercialization.”

While the technology world awaits NIST’s latest “post-quantum” cryptography standards this summer, a parallel effort is underway to also develop cryptosystems that are grounded in quantum technology—what are called quantum-key distribution or QKD systems.

As a result, India, China, and a range of technology organizations in the European Union and United States are researching and developing QKD and weighing standards for the nascent cryptography alternative. And the biggest question of all is how or if QKD fits into a robust, reliable, and fully future-proof cryptography system that will ultimately become the global standard for secure digital communications into the 2030s. As in any emerging technology standard, different players are staking claims on different technologies and implementations of those technologies. And many of the big players are pursuing such divergent options because no technology is a clear winner at the moment.

According to Ciel Qi, a research analyst at the New York-based Rhodium Group, there’s one clear leader in QKD research and development—at least for now. “While China likely holds an advantage in QKD-based cryptography due to its early investment and development, others are catching up,” says Qi.

Two different kinds of “quantum secure” tech

At the center of these varied cryptography efforts is the distinction between QKD and post-quantum cryptography (PQC) systems. QKD is based on quantum physics, which holds that entangled qubits can store their shared information so securely that any effort to uncover it is unavoidably detectable. Sending pairs of entangled-photon qubits to both ends of a network provides the basis for physically secure cryptographic keys that can lock down data packets sent across that network.

Typically, quantum cryptography systems are built around photon sources that chirp out entangled photon pairs—where photon A heading down one length of fiber has a polarization that’s perpendicular to the polarization of photon B heading in the other direction. The recipients of these two photons perform separate measurements that enable both recipients to know that they and only they have the shared information transmitted by these photon pairs. (Otherwise, if a third party had intervened and measured one or both photons first, the delicate photon states would have been irreparably altered before reaching the recipients.)

“People can’t predict theoretically that these PQC algorithms won’t be broken one day.” —Doug Finke, Global Quantum Intelligence

This shared bit the two people on opposite ends of the line have in common then becomes a 0 or 1 in a budding secret key that the two recipients build up by sharing more and more entangled photons. Build up enough shared secret 0s and 1s between sender and receiver, and that secret key can be used for a type of strong cryptography, called a one-time pad, that guarantees a message’s safe transmission and faithful receipt by only the intended recipient.

By contrast, post-quantum cryptography (PQC) is based not around quantum physics but pure math, in which next-generation cryptographic algorithms are designed to run on conventional computers. And it’s the algorithms’ vast complexity that makes PQC security systems practically uncrackable, even by a quantum computer. So NIST—the U.S. National Institute of Standards and Technology—is developing gold-standard PQC systems that will undergird tomorrow’s post-quantum networks and communications.

The big problem with the latter approach, says Doug Finke, chief content officer of the New York-based Global Quantum Intelligence, is PQC is only believed (on very, very good but not infallible evidence) to be uncrackable by a fully-grown quantum computer. PQC, in other words, cannot necessarily offer the ironclad “quantum security” that’s promised.

“People can’t predict theoretically that these PQC algorithms won’t be broken one day,” Finke says. “On the other hand, QKD—there are theoretical arguments based on quantum physics that you can’t break a QKD network.”

That said, real-world QKD implementations might still be hackable via side-channel, device-based, and other clever attacks. Plus, QKD also requires direct access to a quantum-grade fiber optics network and sensitive quantum communications tech, neither of which is exactly commonplace today. “For day-to-day stuff, for me to send my credit card information to Amazon on my cellphone,” Finke says, “I’m not going to use QKD.”

China’s early QKD lead dwindling

According to Qi, China may have originally picked QKD as a focal point of their quantum technology development in part because the U.S. was not directing its efforts that way. “[The] strategic focus on QKD may be driven by China’s desire to secure a unique technological advantage, particularly as the U.S. leads in PQC efforts globally,” she says.

In particular, she points to ramped up efforts to use satellite uplinks and downlinks as the basis for free-space Chinese QKD systems. Citing as a source China’s “father of quantum,” Pan Jianwei, Qi says, “To achieve global quantum network coverage, China is currently developing a medium-high orbit quantum satellite, which is expected to be launched around 2026.”

That said, the limiting factor in all QKD systems to date is their ultimate reliance on a single photon to represent each qubit. Not even the most exquisitely-refined lasers and fiber optic lines can’t escape the vulnerability of individual photons.

QKD repeaters, which would blindly replicate a single photon’s quantum state but not leak any distinguishing information about the individual photons passing through—meaning the repeater would not be hackable by eavesdroppers—do not exist today. But, Finke says, such tech is achievable, though at least 5 to 10 years away. “It definitely is early days,” he says.

“While China likely holds an advantage in QKD-based cryptography due to its early investment and development, others are catching up.” —Ciel Qi, Rhodium Group

“In China they do have a 2,000-kilometer network,” Finke says. “But it uses this thing called trusted nodes. I think they have over 30 in the Beijing to Shanghai network. So maybe every 100 km, they have this unit which basically measures the signal... and then regenerates it. But the trusted node you have to locate on an army base or someplace like that. If someone breaks in there, they can hack into the communications.”

Meanwhile, India has been playing catch-up, according to Satyam Priyadarshy, a senior advisor to Global Quantum Intelligence. Priyadarshy says India’s National Quantum Mission includes plans for QKD communications research—aiming ultimately for QKD networks connecting cities over 2,000-km distances, as well as across similarly long-ranging satellite communications networks.

Priyadarshy points both to government QKD research efforts—including at the Indian Space Research Organization—and private enterprise-based R&D, including by the Bengaluru-based cybersecurity firm QuNu Labs. Priyadarshy says that QuNu, for example, has been working on a hub-and-spoke framework named ChaQra for QKD. (Spectrum also sent requests for comment to officials at India’s Department of Telecommunications, which were unanswered as of press time.)

“A hybrid of QKD and PQC is the most likely solution for a quantum safe network.” —Satyam Priyadarshy, Global Quantum Intelligence

In the U.S. and European Union, similar early-stage efforts are also afoot. Contacted by IEEE Spectrum, officials from the European Telecommunications Standards Institute (ETSI); the International Standards Organization (ISO); the International Electrotechnical Commission (IEC); and the IEEE Communications Society confirmed initiatives and working groups that are now working to both promote QKD technologies and emergent standards now taking shape.

“While ETSI is fortunate to have experts in a broad range of relevant topics, there is a lot to do,” says Martin Ward, senior research scientist based at Toshiba’s Cambridge Research Laboratory in England, and chair of a QKD industry standards group at ETSI.

Multiple sources contacted for this article envisioned a probable future in which PQC will likely be the default standard for most secure communications in a world of pervasive quantum computing. Yet, PQC also cannot avoid its potential Achilles’ heel against increasingly powerful quantum algorithms and machines either. This is where, the sources suggest, QKD could offer the prospect of hybrid secure communications that PQC alone could never provide.

“QKD provides [theoretical] information security, while PQC enables scalab[ility],” Priyadarshy says. “A hybrid of QKD and PQC is the most likely solution for a quantum safe network.” But he added that efforts at investigating hybrid QKD-PQC technologies and standards today are “very limited.”

Then, says Finke, QKD could still have the final say, even in a world where PQC remains preeminent. Developing QKD technology just happens, he points out, to also provide the basis for a future quantum Internet.

“It’s very important to understand that QKD is actually just one use case for a full quantum network,” Finke says.

“There’s a lot of applications, like distributed quantum computing and quantum data centers and quantum sensor networks,” Finke adds. “So even the research that people are doing now in QKD is still very, very helpful because a lot of that same technology can be leveraged for some of these other use cases.”

As the world’s 5G rollout continues with its predictable fits and starts, the cellular technology is also starting to move into a space already dominated by another wireless tech: Wi-Fi. Private 5G networks—in which a person or company sets up their own facility-wide cellular network—are today finding applications where Wi-Fi was once the only viable game in town. This month, the Newbury, England–based telecom company Vodafone is releasing a Raspberry Pi–based private 5G base station that it is now being aimed at developers, who might then jump-start a wave of private 5G innovation.

“The Raspberry Pi is the most affordable CPU[-based] computer that you can get,” says Santiago Tenorio, network architecture director at Vodafone. “Which means that what we build, in essence, has a similar bill of materials as a good quality Wi-Fi router.”

The company has teamed with the Surrey, England–based Lime Microsystems to release a crowd-funded range of private 5G base-station kits ranging in price from US $800 to $12,000.

“In a Raspberry Pi—in this case, a Raspberry Pi 4 is what we used—then you can be sure you can run that anywhere, because it’s the tiniest processor that you can have,” Tenorio says.

Santiago Tenorio holds one of Lime Microsystems’ private 5G base-station kits.Vodafone

Private 5G for Drones and Bakeries

There are a range of reasons, Tenorio says, why someone might want their own private 5G network. At the moment, the scenarios mostly concern companies and organizations—although individual expert users could still be drawn to, for instance, 5G’s relatively low latency and network flexibility.

Tenorio highlighted security and mobility as two big selling points for private 5G.

A commercial storefront business, for instance, might be attracted to the extra security protections that a SIM card can provide compared to password-based wireless network security. Because each SIM card contains its own unique identifier and encryption keys, thereby also enabling a network to be able to recognize and authorize each individual connection, Tenorio says private 5G network security is a considerable selling point.

Plus, Tenorio says, it’s simpler for customers to access. Envisioning a use case of a bakery with its own privately deployed 5G network, he says, “You don’t need a password. You don’t need a conversation [with a clerk behind a counter] or a QR code. You simply walk into the bakery, and you are into the bakery’s network.”

As to mobility, Tenorio suggests one emergency relief and rescue application that might rely on the presence of a nearby 5G station that causes devices in its range to ping.

Setting up a private 5G base station on a drone, Tenorio says, would enable that drone to fly over a disaster area and, via its airborne network, send a challenge signal to all devices in its coverage area to report in. Any device receiving that signal with a compatible SIM card then responds with its unique identification information.

“Then any phone would try to register,” Tenorio says. “And then you would know if there is someone [there].”

Not only that, but because the ping would be from a device with a SIM card, the private 5G rescue drone in the above scenario could potentially provide crucial information about each individual, just based on the device’s identifier alone. And that user-identifying feature of private 5G isn’t exactly irrelevant to a bakery owner—or to any other commercial customer—either, Tenorio says.

“If you are a bakery,” he says, “You could actually know who your customers are, because anyone walking into the bakery would register on your network and would leave their [International Mobile Subscriber Identity].”

Winning the Lag Race

According to Christian Wietfeld, professor of electrical engineering at the Technical University of Dortmund in Germany, private 5G networks also bring the possibility of less lag. His team has tested private 5G deployments—although, Wietfeld says that they haven’t yet tested the present Vodafone/Lime Microsystem base station—and have found private 5G to provide reliably better connectivity.

Wietfeld’s team will present their research at the IEEE International Symposium on Personal, Indoor and Mobile Radio Communications in September in Valencia, Spain. They found that private 5G can deliver connections up to 10 times as fast as connections in networks with high loads, compared to Wi-Fi (the IEEE 802.11 wireless standard).

“The additional cost and effort to operate a private 5G network pays off in lower downtimes of production and less delays in delivery of goods,” Wietfeld says. “Also, for safety-critical use cases such as on-campus teleoperated driving, private 5G networks provide the necessary reliability and predictability of performance.”

For Lime Networks, according to the company’s CEO and founder Ebrahim Bushehri, the challenge comes in developing a private 5G base station that maximized versatility and openness to whatever kinds of applications developers could envision—while still being reasonably inexpensive and retaining a low-power envelope.

“The solution had to be ultraportable and with an optional battery pack which could be mounted on drones and autonomous robots, for remote and tactical deployments, such as emergency-response scenarios and temporary events,” Bushehri says.

Meanwhile, the crowdfunding behind the device’s rollout, via the website Crowd Supply, allows both companies to keep tabs on the kinds of applications the developer community is envisioning for this technology, he says.

“Crowdfunding,” Bushehri says, “Is one of the key indicators of community interest and engagement. Hence the reason for launching the campaign on Crowd Supply to get feedback from early adopters.”

A short-haul aircraft in the United Kingdom recently became the first airborne platform to test delicate quantum technologies that could usher in a post-GPS world—in which satellite-based navigation (be it GPS, BeiDou, Galileo, or others) cedes its singular place as a trusted navigational tool. The question now is how soon will it take for this quantum tomorrow to actually arrive.

But is this tech just around the corner, as its proponents suggest? Or will the world need to wait until the 2030s or beyond, as skeptics maintain. Whenever the technology can scale up, potential civilian applications will be substantial.

“The very first application or very valuable application is going to be autonomous shipping,” says Max Perez, vice president for strategic initiatives at the Boulder, Colo.–based company Infleqtion. “As we get these systems down smaller, they’re going to start to be able to address other areas like autonomous mining, for example, and other industrial settings where GPS might be degraded. And then, ultimately, the largest application will be generalized, personal autonomous vehicles—whether terrestrial or air-based.”

The big idea Infleqtion and its U.K. partners are testing is whether the extreme sensitivity that quantum sensors can provide is worth the trade-off of all the expensive kit needed to miniaturize such tech so it can fit on a plane, boat, spacecraft, car, truck, or train.

Turning Bose-Einstein Condensates Into Navigational Tools

At the core of Infleqtion’s technology is a state of matter called a Bose-Einstein condensate (BEC), which can be made to be extremely sensitive to acceleration. And in the absence of an external GPS signal, an aircraft that can keep a close tally on its every rotation and acceleration is an aircraft that can infer its exact location relative to its last known position.

As Perez describes it—the company has not yet published a paper on its latest, landmark accomplishment—Infleqtion’s somewhat-portable BEC device occupies 8 to 10 rack units of space. (One rack unit represents a standard server rack’s width of 48.3 centimeters and a standard server rack depth of 60–100 cm.)

Scientists tested delicate Bose-Einstein condensates in their instruments, which could one day undergird ultrasensitive accelerometers.Qinetiq

In May, the company flew its rig aboard a British Aerospace 146 (BAe 146/Avro RJ100) tech demonstrator aircraft. Inside the rig, a set of lasers blasted a small, supercooled cloud of rubidium atoms to establish a single quantum state among the atoms. The upshot of this cold atom trap is to create ultrasensitive quantum conditions among the whole aggregation of atoms, which is then a big enough cloud of matter to be able to be manipulated with standard laboratory equipment.

Using the quantum wave-particle duality, in which matter behaves both like tiny billiard balls and wave packets, engineers can then use lasers and magnetic fields to split the BEC cloud into two or more coherent matter-wave packets. When later recombined, the interference patterns of the multiple wave packets are studied to discover even the most minuscule accelerations—tinier than conventional accelerometers could measure—to the wave packets’ positions in three-dimensional space.

That’s the theoretical idea, at least.

Real-World Conditions Muddy Timetables

In practice, any BEC-based accelerometer would need to at least match the sensitivity of existing, conventional accelerometer technologies.

“The best inertial systems in the world, based on ring laser gyroscopes, or fiber-optic gyroscopes, can...maintain a nautical mile of precision over about two weeks of mission,” Perez says. “That’s the standard.”

The Infleqtion rig has provided only a proof of principle for creating a manipulable BEC state in a rubidium cloud, Perez adds, so there’s no one-to-one comparison yet available for the quantum accelerometer technology. That said, he expects Infleqtion to be able to either maintain the same nautical-mile precision over a month or more mission time—or, conversely, increase the sensitivity over a week’s mission to something like one-tenth of a nautical mile.

The eventual application space for the technology is vast, says Doug Finke, chief content officer at the New York City–based market research firm Global Quantum Intelligence.

“Quantum navigation devices could become the killer application for quantum-sensing technology,” Finke says. “However, many challenges remain to reduce the cost, size, and reliability. But potentially, if this technology follows it similar path to what happened in computing, from room-size mainframes to something that fits inside one’s pocket, it could become ubiquitous and possibly even replace GPS later this century.”

The timeframe for such a takeover remains an unanswered question. “It won’t happen immediately due to the engineering challenges still to be resolved,” Finke says. “And the technology may require many more years to reach maturation.”

Dana Goward, president of the Alexandria, Va.–based Resilient Navigation and Timing Foundation, even ventures a prediction. “It will be 10 to 15 years at least before we see something that is practical for broad application,” he says.

Perez says that by 2026, Infleqtion will be testing the reliability of its actual accelerometer technology—not just setting up a BEC in midflight, as it did in May. “It’s basically trading off getting the technology out there a little faster versus something that is more precise for more demanding applications that’ll be just behind that,” Perez says.

UPDATE 4 June 2024: The story was updated to modify the accuracy estimate for the best inertial navigation systems today—from one nautical mile per one-week mission (as a previous version of this story stated) to one nautical mile per two-week mission.