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Biomedical Optics & Medical Imaging

Quantum technologies: Accelerating toward commercialization

Devices using quantum technologies are reaching milestones.

6 April 2018, SPIE Newsroom. DOI: 10.1117/2.2201804.04
Quantum Tech_cover of SPIE Pro

In 2013, a boutique watchmaker and a military contractor put their heads together and built the first atomic wristwatch ever.

The timepiece, produced by Bathys Hawaii Watches (USA), exploits the same physical mechanism as the current international time standard, a precise atomic clock that will be accurate to the second for 1.4 million years. Like the standard, the wristwatch relies on the quantum mechanical properties of vaporized cesium atoms and a laser. Unlike the standard, it runs on a rechargeable lithium battery and only has a precision of 1 second per millennium.

Bathys sold a limited number of them at $6,000 apiece on the crowdfunding platform Kickstarter.

About the size of a playing card, it is bulky for a wristwatch. But it's still a design milestone, a direct descendant of the first cesium clock built in 1955 by researchers in the UK. These clocks used to be huge devices - taller than a human - and could function only in the extremely stabilized conditions of a lab. Researchers have shrunk such clocks to fit not just on wrists, but chips. What's more, they've proven useful in unexpected ways: for example, they are crucial to the accuracy of GPS satellites.

Other devices using quantum technologies - cryptography systems, magnetometers, and computers - have not been around as long, but they are reaching milestones of their own.

Photon Force SPAD camera
Foton Force has developed time-resolved single-photon avalanche photodiode (SPAD) cameras that are finding applications in LIDAR, quantum technologies, and fluorescence spectroscopy. Credit: Foton Force

Like the atomic clock, these devices also exploit quantum mechanics, the bizarre laws that microscopic particles obey. Researchers are creating these devices by building new hardware - lasers, single-photon generators, etc. - and inventing techniques to manipulate particles on this tiny scale. In 2015, 7000 people worked on quantum technologies worldwide, with a combined annual budget of 1.5 billion euros, according to McKinsey, a global management consulting firm.

The devices range vastly in commercial maturity. But the decades-long investment in basic quantum research could start to pay off soon.

Quantum cryptography
Quantum cryptography is one of the more developed quantum technologies, says physicist Tim Spiller, who directs the Quantum Communications Hub in the UK. Commercial systems for limited applications have been available for purchase for over a decade and are currently offered by a variety of companies, including ID Quantique (Switzerland), MagiQ Technologies (USA), and QuantumCTek (China). In September 2017, Chinese and Austrian physicists successfully used these systems, along with a satellite, to participate in the first ever quantum-encrypted, intercontinental conference call between Beijing and Vienna.

These systems theoretically promise absolute security, although they have yet been unable to fully achieve it under real-world conditions. Theoretically, a quantum cryptography protocol exploits a strange quantum rule about measurement. The rule says that if you measure a property of a quantum particle, you instantly change that property. The act of measurement corrupts the measurement.

The protocols are complicated, but the gist is this: If someone tries to intercept a quantum signal, they instantly alter the signal in a detectable way. For example, say you want to send a quantum-secured message. You encrypt it using a binary string, or key, encoded in photon polarizations.

Before you send the message, you share this key with your intended recipient. The two of you then share part of the key publicly. If someone had intercepted the signal, your keys would be mismatched in a particular statistical way. You would immediately know not to use the key.

Intel's 49-qubit test chip
Intel's 49-qubit test chip. Credit: Walden Kirsch/Intel

For the past decade, researchers and engineers have been implementing these protocols in real-world situations. Switzerland's government, for example, has quantum-encrypted parts of its election infrastructure since 2007. In 2016, China launched a satellite for quantum cryptography, and it plans to launch more to create an international network in the next few years. Spiller's Quantum Communications Hub, collaborating with Toshiba, has built a small quantum network in Cambridge (UK) that they plan to connect to other cities in the UK in the next year.

However, they have found it challenging to transmit the quantum keys long distances. Quantum signals die out in fiber and in free space after a few hundred kilometers.

So, the researchers and engineers began integrating quantum technology into traditional fiber networks. The Chinese network, for example, converts quantum signals into classical information on their satellite and at several stations on the ground. The UK network will be a hybrid network, also. This has the added advantage of lowering infrastructure costs.

"We're not going to lay a whole new network from scratch," Spiller says. "We are going to leverage off what already exists."

Hybrid networks, though, diminish the absolute security of the technology. Every time the signal is converted into classical information, eavesdroppers can use conventional methods to hack into the system. Researchers call these conversion stations "trusted relays" or "trusted nodes" because to believe in the security of the system, you must trust they haven't been hacked.

Consequently, researchers are working to develop special amplifiers called quantum repeaters in the hopes that they can build a completely quantum network. However, these technologies "are still very much at the laboratory experiment level," says Spiller.

Researchers are considering a variety of materials for these devices, says physicist Kai-Mei Fu of the University of Washington (USA). One possibility is a defect in a crystal such as diamond or silicon carbide. You can program the defect with a laser, and the information will last a relatively long time because it is protected by the surrounding crystal structure. Ultracold ions and solids known as rare-earth-doped crystals are also potential candidates because of their ability to preserve quantum information.

However, basic engineering challenges remain. It is difficult to integrate multiple crystal defects onto a single device, Fu says. In addition, ions only operate at low temperatures in ultra-high vacuum, which isn't practical in a device.

In the next decade, Fu thinks that an entirely quantum network - without classical conversions - will be technically feasible. But even though governments and banks have indicated interest in these products, it's unclear whether they'll have the necessary demand. "It'll be a matter of who really wants it," she says.

Quantum magnetic sensors
As researchers studied crystal defects for quantum memories, they inadvertently discovered a new use for them: magnetometry. If you shoot a laser at a diamond with a defect called a nitrogen vacancy center, that diamond will then emit different amounts of light depending on the strength of the magnetic field it is in. "You can bring it really close to a material and sense the magnetic field from the material," Fu says.

An academic group led by physicist Ronald Walsworth at Harvard University (USA) has used these nitrogen vacancy diamonds to image magnetic fields produced by animal neurons. The advantage of the diamonds is that they can be operated at room temperature and held very close to the object being imaged. This is in contrast with the most sensitive commercial magnetometers today, known as SQUID magnetometers, which are bulky and must be operated at a temperature near absolute zero.

Company spinoffs of academic labs, such as Quantum Diamond Technologies and ODMR Technologies, are developing quantum magnetic sensors for medical imaging, but they are not commercially available yet.

The quantum computer
Many companies, including Google, IBM, Intel, and Microsoft, have been racing to build the first quantum computer that can beat a conventional one. To that end, they've developed quantum bits, or qubits, out of various materials. Google and IBM, for instance, are using qubits made of superconducting circuits, while startup IonQ is betting on trapped ions.

Typical ion trap used in quantum information and computing labs at University of Maryland.
Typical ion trap used in quantum information and computing labs at University of Maryland. Ions are confined by electric fields in the central region, here indicated by a flare. Credit: E. Edwards, JQI.

They are also working to connect as many of those qubits as possible. IBM demonstrated a record 50 qubits in 2017. "I've been in this field for almost 25 years," says physicist Christopher Monroe of the University of Maryland (USA), who cofounded IonQ. "The last three or four years have been the most exciting because of industry involvement," he says.

They're working to build a computer that processes not simple 1s and 0s, but weighted combinations, or superpositions, of 1s and 0s. This is akin to Schrödinger's cat, which is a weighted combination of both dead and alive. Eventually, a quantum computer should be able to execute many types of algorithms faster than a conventional computer, such as simulating quantum processes like photosynthesis or factoring large prime numbers.

To build their quantum computer, IonQ is collaborating with US government contractor Harris. Harris produces an acousto-optic modulator (AOM), a device that can precisely change the phase, amplitude, and frequency of a laser using sound waves. Harris first designed the device for the semiconductor industry, to control the etching process. A revamped AOM now helps write the ion qubits for IonQ.

Harris is also considering other quantum computing problems related to US national security. Engineer Catheryn Logan of Harris thinks that in the future, people will likely not own their personal quantum computers and instead purchase computational time on a communal one.

"We're thinking, how would that get applied to classified work?" she says. "A government agency is not going to buy time on some public-use quantum computer; they'll build their own. We're trying to understand what that looks like."

M Squared is developing a commercial quantum gravimeter. Credit M Squared.
M Squared is developing a commercial quantum gravimeter. Credit M Squared.

Even as they look ahead, researchers acknowledge that the current quantum computers can't accomplish any useful tasks. While many companies have demonstrated specific algorithms with connected qubits, the algorithms don't accomplish any practical tasks and just demonstrate that the researchers have control over the qubits. The technology is still decades away from being translated into broadly useful devices such as the desktops and laptops used today.

That hasn't deterred the hype. In November 2017, IBM promised to put a 20-qubit quantum computer online for customers to use, following a 5-qubit version already available.

Venture capital firms New Enterprise Associates and GV, formerly Google Ventures, invested in IonQ about a year ago. IonQ, which formed in late 2015 as a spinoff of two academic labs, specifically looked for patient investors planning for the long term, on the scale of a decade and longer, Monroe says. "They understand the field is a speculative one," he says. "Venture-funded firms often don't succeed, but when they do, they can succeed big. That's certainly the attitude of our investors."

Precision optical clocks
Atomic clocks are undergoing yet another evolution. The most precise systems today rely on a system known as an optical lattice nearly 10,000 times more precise than the conventional cesium clock. The most precise clock today, a strontium optical lattice clock developed in 2017 by US researchers at the University of Colorado, Boulder and the National Institute of Standards and Technology (NIST), will be accurate to the second for over 15 billion years, longer than the age of the universe.

Atomic clocks keep time by counting the extremely consistent cycles of radiation emitted when a laser quantum mechanically excites an atom. The old cesium clocks emitted microwave radiation, which oscillates at about 9 billion times per second. The new record-breaking clock is more precise partly because it uses strontium atoms, which emit near-infrared light that oscillates more than 10,000 times faster.

Researchers around the world are currently working to miniaturize these clocks. Recently, researchers at Germany's National Metrology Institute created the first-ever portable optical lattice clock, loaded it in a trailer, and took it inside a cave on the Germany-Italy border.

They want to use the portable clock to measure not time - but elevation. Because the clock ticks so precisely, you can actually measure the effect of gravity on it.

According to Einstein's theory of general relativity, a clock closer to Earth's surface - one in a stronger gravitational field, that is - will tick slower. Combined with satellite data, these portable clocks could be used to monitor sea-level rise, for example.

Like the clock, other quantum technologies could end up in unexpected applications. It's unclear what secrets quantum cryptography will secure; what magnetic fields quantum magnetometers will find; what algorithms quantum computers will execute.

The challenge ahead is to figure out who will use these technologies - and what exactly they can do with them.

-Sophia Chen is a freelance science writer based in Tucson, AZ (USA). This article was originally published in the April 2018 edition of SPIE Professional magazine.


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