We are in midst of the second quantum revolution moving from merely computing quantum properties of systems to exploiting them. Researchers are developing new capabilities in secure communication, ultra-sensitive and high signal to noise physical sensing of the environment and Quantum Information Science (QIS). Yet many scientists believe that quantum will enjoy its first real commercial success in sensing. That’s because sensing can take advantage of the very characteristic that makes building a quantum computer so difficult: the extraordinary sensitivity of quantum states to the environment.
Quantum sensors are measuring device that takes advantage of quantum correlations, such as states in a quantum superposition or entanglement, for better sensitivity and resolution than can be obtained by classical systems. A quantum sensor can measure the effect of the quantum state of another system on itself. The mere act of measurement influences the quantum state and alters the probability and uncertainty associated with its state during measurement. For decades, quantum measurements have been used in metrology to define fundamental constants such as time. More recently, this approach is being applied to sensing.
When measurements are based on quantum phenomena, such as the energy difference between two well-defined quantum states, sensors have the ability to reach unprecedented precision and accuracy that doesn’t drift over time. High sensitivity and stability in combination with a small form factor provide transformational capabilities with applications spanning from GPS-free global navigation and cryogen-free high-precision magnetometry to sensing within mesoscale structure and measurements of individual nuclear or electron spins.
Quantum sensors include atomic clocks, single-photon detectors, PAR sensors, quantum LiDAR and quantum radar, gravity sensors, atomic interferometers, magnetometers, quantum imaging devices, spin-qubit-based sensors, and quantum rotation sensors. We also take a look at materials used for quantum sensors, especially diamond and graphene
Quantum sensors also useful in many military applications such as through wall imaging, detecting deeply buried structures and stealth airplanes. In particular, quantum radar can be used to detect targets that cannot be discerned through conventional radar, and quantum navigation similarly leverages quantum properties to create a precise form of positioning system that may eventually replace GPS.
Quantum sensing has become a distinct and rapidly growing branch of research within the area of quantum science and technology, with the most common platforms being spin qubits, trapped ions and flux qubits. Quantum sensors are just becoming commercially available. Numerous scientists working on quantum sensors have set up companies to commercialize their technology, but few have actual products on the market.
Whether they are responding to the gravitational pull of buried objects or picking up magnetic fields from the human brain, quantum sensors can detect a wide range of tiny signals from the world around us. Kai Bongs, a physicist at Birmingham University, U.K., believes that gravity-measuring quantum sensors in particular “will become more widespread quite quickly,” with a potential market of perhaps US$1 billion a year. The global quantum sensors market should grow from $161.0 million in 2019 to $299.9 million by 2024 with a compound annual growth rate (CAGR) of 13.2% during the period, 2019-2024. There is also emerging technology – such as quantum photonics – that will lead to new kinds of sensor products being developed in the near future.
For over 30 years, academics have been exploring the strange effects of quantum superposition – the principle that 2 or more quantum states can be added together to result in another valid quantum state – to measure gravity. This is done by comparing wave-particle duality – the concept that quantum entities can be described both as particles and waves – in atoms of the element rubidium. By comparing wave-particle duality with a laser beam, the instrument will be able to detect very small changes in the way atoms fall freely in a vacuum, determining the local strength of gravity. If the measurement is sensitive enough, it will be able to detect if there are voids, pipes, tunnels and oil and gas reserves in the ground beneath your feet.
Atom interferometers could also be used to build navigation devices that continue to work even when contact with GPS satellites is lost, as can happen in a tunnel or, more ominously, when signals are deliberately jammed. Keeping on course in this way relies on dead reckoning, the use of accelerometers and gyroscopes to continuously update a vehicle’s position, orientation and velocity with respect to a known starting point.
Like spring gravimeters, conventional accelerometers experience drift, as their pendula warp over time. In contrast, quantum accelerometers—essentially gravimeters with their laser beams flipped along the acceleration axis—are very stable. Although the atoms’ finite free-fall time and need for preparation prevent continuous operation, which is often provided by conventional accelerometers, they enable proper calibration.
Quantum gyroscopes, meanwhile, work by generating a phase difference between atom waves propagating in opposite directions around a rotating ring. Such technology has been developed by AOSense, a company in Sunnyvale, Calif., USA, set up in 2004 by atomic physicist Mark Kasevich and two colleagues at Stanford University, USA. Often working with the U.S. military, the firm built prototype gradiometers, gyroscopes and accelerometers for the Defense Advanced Research Projects Agency (DARPA). The aim, according to a 2014 story in Physics Today, was to make inertial measurement units that could fit on a fingertip. But in the end, Kasevich says, the necessary lasers and optical modulators couldn’t be made small enough to shrink gyroscopes below “about 100 cm3.”
Making atomic sensors competitive with existing technology is “a struggle,” according to Kasevich, because the subsystems that they rely on, such as lasers and vacuum chambers, are large and complex, and have not had their costs driven down by mass markets. Trying to shrink gyroscopes in particular incurs “crazy development costs,” says Pereira Dos Santos. One option would be to guide rather than drop atoms, but that, he says, is “very exploratory … and it might never work.”
But another type of quantum technology has simple subsystems and can be built using standard materials-science techniques: nitrogen–vacancy (NV) centers. These are atom-like defects in a synthetic diamond crystal consisting of a nitrogen atom and a gap in place of two carbon atoms. NV centers can emit red light when excited by green, but the probability of doing so depends on the spin states of their electrons. By placing the spin states in a superposition, microwaves with just the right frequency can change the emission intensity.
Crucially, this quantum state can persist for up to a millisecond at room temperature, thanks to the stiff diamond lattice that shields the NV centers from vibrations. And, because changes in the local magnetic field will change the spacing of the spin states and knock the microwave frequency off-resonance—with the change proportional to the field strength—NV centers could potentially make extremely sensitive magnetometers. The system is also sensitive to variations in electric field, strain and temperature, as these change the distance between atoms and, again, shift the resonance.
Several start-up companies are looking to commercialize NV technology, in areas such as biomedicine (see “Probing neurons and tumors,” p. 30), while some multinationals are also entering the fray. These include the German engineering giant Bosch, which is building a prototype NV sensor to monitor charging and prevent excess currents in car batteries. The French electronics company Thales, meanwhile, is applying magnetic field gradients across NV diamond crystals to identify frequency components in unknown microwave spectra.
According to Thales’ head of applied quantum physics, Thierry Debuisschert, 5G network operators could use this technology, for example, to prevent interference between neighboring cell towers. But he says that it will likely take several years to overcome technical and commercial obstacles, such as working out how best to collect the faint red light emitted by the crystal. Likewise, Bosch researcher Robert Roelver says that his company probably won’t market a device for another five to ten years.
Researchers at U.S. defense firm Lockheed Martin also face hurdles in commercializing an innovative navigation instrument. The roughly foot-long NV-based device navigates by picking up tiny anomalies in the Earth’s magnetic field that have previously been mapped. Project leader Michael DiMario explains that more than five years of work have yielded “very promising results” on land, at sea and in the air—but also unforeseen problems. “I can’t really say when it will go to market,” he says.
While cold-atom and NV sensors rely on superposition, some sensors are designed to exploit another strange quantum phenomenon, entanglement. One of these technologies is quantum radar. Based on a theoretical scheme by physicist Seth Lloyd, this involves bouncing one half of a series of entangled-photon pairs off an object and then comparing the returning photons with those held back. The idea is to distinguish the radiation originally sent out from strong sources of noise, to spot otherwise undetectable objects such as stealth aircraft, and to keep the radar operators hidden.
Jonathan Baugh of the University of Waterloo in Canada is developing a near-infrared device to produce pairs of entangled photons on demand, which he says should be ready for field testing “a few years” from now. Although this will require an additional device to convert the output to microwave frequencies, it might in the end only need quantum statistics rather than entanglement per se. “If you always produce two photons at almost exactly the same time, you can use the timing correlation,” he says.
Quantum information and integrated nanosystems at MIT
Quantum sensing at Lincoln Laboratory focuses on devices that exceed the capability of their classical counterparts. Their first sensors take advantage of the nitrogen vacancy (NV), a quantum system embedded in a solid-state diamond. These nitrogen-vacancy pairs, or color centers as they are often called, have atom-like quantized energy levels that can be manipulated to sense electromagnetic fields, rotation, temperature, pressure, stress, and even to measure time (frequency). While precision quantum mechanical measurements typically sprawl across several optical tables or require cryogen dewars, devices based on color centers have the promise of a room-temperature, all-solid-state solution to quantum sensing.
When a magnetic field is present, the energy levels of this atom-like system get split and the shift can be read out to determine the magnitude of the externally applied field. Compared to other color centers, the NV’s uniqueness stems from its ability to be addressed and read out optically; this is known as optically detected magnetic resonance (ODMR). For the nitrogen vacancy in diamond, a green laser initiates the atomic-like system into a well-known state, RF fields near 3 GHz control the state coherence, and red fluorescence or absorption is read out to make the measurement.
Recent work focuses on ensemble NV-based magnetometers employing N unentangled color centers to realize a factor of up to √N improvement in sensitivity. “In order to realize fully this signal enhancement, we are developing new techniques to excite efficiently and to collect fluorescence from large NV ensembles.”
Current goals focus on improving the diamond magnetometer and gradiometer sensitivity, enhancing its coherence, improving its spatial resolution, and devising strategies to achieve sensitivity beyond the Heisenberg limit. From quantum non-demolition measurement to dynamical decoupling and spin squeezing, techniques from quantum information science are critical in achieving these goals.
A Chip-Scale Platform for Quantum Sensors
Spectroscopy of atomic vapors serves as the foundation for quantum sensors of magnetic and electric fields, time, length and other quantities. But it’s been tough to bring the scheme down to the scale of silicon-photonic chips for devices useful in field and industrial settings.
Now, researchers at the U.S. National Institute of Standards and Technology (NIST) have developed a prototype, 1-cm3 integrated photonic device that can perform precision spectroscopy on an ensemble of warm rubidium atoms. The team believes that the device could constitute a “miniature toolkit” for building compact, mass-producible quantum-based sensors for use in communications, navigation, instrument calibration and other fields.
Getting past bulk optics
Ensembles of atoms, trapped as vapors in small cells, are exquisitely sensitive to external fields or perturbations, and many sensor devices already use light, and specifically precision spectroscopy, to probe the quantum states of such ensembles. Those devices, however, tend to be built by hand with bulk optics.
Efforts to integrate precision spectroscopy of atomic vapors onto smaller-footprint devices have generally taken one of two approaches: sending light through a small waveguide, and having the evanescent light near the waveguide interact with surrounding atoms; or putting the atoms to be probed within a hollow-core waveguide itself. The limited overlap of the optical mode with the vapor, however, makes the former approach a poor fit for precision spectroscopy, according to the NIST team. The hollow-core-waveguide scheme, meanwhile, suffers from complications related to the presence of multiple modes in the fiber, which can lead to frequency shifts that muddy the signal.
For the new device, the NIST team opted for a third way: one that packages the warm atoms to be probed in a 27-mm3 micromachined closed cell, and uses CMOS-compatible, 300-nm-wide silicon nitride (Si3N4) waveguides to deliver the light to the atoms. A key issue the team needed to address in that geometry was how to convert the single-mode light from the narrow waveguide to a wider light field that would interact with enough of the atoms in the cell to return a good signal. The researchers solved the problem by attaching a specially designed “extreme mode converter” apodized grating to the end of the Si3N4 waveguide, where it couples the fiber light mode to free space.
The grating radically expands the mode’s diameter from 500 nm in the fiber to 120 microns in free space—while still maintaining the beam’s single-mode characteristics. The free-space beam thus passes through the cell with a large enough cross-section to probe the energy-level transitions of roughly 100 million Rb atoms, while still avoiding the potential confusion arising from overlap of multiple optical modes. After passing through the vapor cell, a portion of the beam is bounced via a reflective neutral-density filter to interact with a probe beam and create a saturated-absorption spectrometer.
Cold molecular ions may soon prove useful to quantum technology
Trapped and laser-cooled atomic ions is one of the most successful platforms for the development of quantum technology (QT),” says Prof. Michael Drewsen of Aarhus University’s Department of Physics and Astronomy. “In comparison, the complexity of molecular ions have so far made them an unnecessary complication. However, with the growing control of cold molecular ions, their richer structure and the greater diversity of molecules can actually be turned into an advantage for the further development of ion trap-based QT by picking out the species with the right properties.”
In other words, cold and trapped molecular ions could expand the realm of quantum technology, with potential applications in the likes of ultra-sensitive mass spectrometry, ultra-resolution spectroscopy, the cooling of macromolecular ions in the gas phase, or chemical processes at very low temperature.
As Prof. Drewsen points out, a large part of the COMIQ project, which he coordinated until November 2017, has been devoted to increasing the quantum state control and manipulation of individual molecular ion species – a key step towards the use of molecular ions in QT. In addition, the research has shed light on how trapped cold molecular ions interact with their environment, in turn leading to a better understanding of the practical problems to be tackled in the implementation of molecular ion based QT.
Quantum trick blocks background ‘chatter’ in sensing devices
Researchers led by Professor Michael J. Biercuk from the University of Sydney, in collaboration with Dartmouth College and Johns Hopkins Applied Physics Laboratory in the US, has developed quantum control techniques enabling a new generation of ultra-sensitive sensors that can identify tiny signals while rejecting background noise down to theoretical limits.
In order to obtain and analyze signals, measurement protocols are set in place. Over the years, these protocols have lagged behind the advancement of electronic devices. The disparity has led to a phenomenon known as “spectral leakage,” which occurs when quantum sensors return unclear results. By using improved sensor hardware, the new control protocols have reduced spectral leakage by several orders of magnitude, according to the researchers.
“By applying the right quantum controls to a qubit-based sensor, we can adjust its response in a way that guarantees the best possible exclusion of the background clutter – that is, the other voices in the room,” said Professor Biercuk, a chief investigator at the ARC Centre of Excellence for Engineered Quantum Systems.
The experiments, using trapped atomic ions, have reduced spectral leakage by many orders of magnitude over conventional methods. Professor Biercuk said in certain circumstances, the methods they have developed are up to 100 million times better at excluding this background.
Our approach is relevant to nearly any quantum sensing application and can also be applied to quantum computing as it provides a way help identify sources of hardware error. This is a major advance in how we operate quantum sensors,” says Professor Biercuk. The team believes the new control protocols can prove useful in medical imaging applications. The defense and security sector can also benefit, aiding systems that use quantum-enhanced magnetometers.
Global quantum sensors market
The global quantum sensors market is still in the early stages of growth and is attracting significant investments from market participants due to anticipated growth. Market participants are investing in the development of new products to explore the potential applications of quantum sensing. Thus, the increasing investments in the market will drive the quantum sensor market growth during the forecast period. Rising investments in quantum technology by market participants are expected to boost market growth. Also, the growing number of strategic partnerships in the market are anticipated to fuel the growth of the quantum sensors market.
Increasing investments in quantum technology by various market players and growing research and development activities in the field of quantum sensing are major driving factors behind the growth of the market. Increasing research and developmental activities related to quantum technology is expected to have ample opportunities in a different field such as military, construction industry, etc. Features such as high credibility and accuracy are making this technology accessible across various sectors.
Growing adoption of quantum sensing solutions in various industries and applications such as material science and quantum physics, increasing developments of quantum gravity sensors, rising demand of quantum sensors to monitor volcanoes to give advanced warning of volcanic activity, a surge in the adoption of quantum sensors in cars to detect pedestrians 100m away or a few metres away and increased demand of quantum sensor from military and defence industry is expected to improve the growth of the market.
However, challenges such as quantum decoherence, the inconsistency between separating the responsive quantum states from external conflicts, and reliance on only some key providers are major restraining factors that could hamper the growth of the market.
Countries are giving thrust to Quantum technology as it is expected to have significant implications for multiple aspects of future military operations. And, China is focused to utilize this technology for its military applications and aimed to become a leader in quantum information science. For instance, in September 2016, Chinese scientists announced their creation of a single-photon quantum radar, which takes advantage of entanglement between photon pairs, those were capable of detecting targets up to 100 kilometers away with high accuracy.
For instance, in October 2018, the US Army scientists created innovative quantum sensors to detect the communication signals over the radio frequency spectrum. This quantum sensor uses high energized, super-sensitive atoms named as Rydberg atoms. This quantum sensor provides military soldiers an approach to sense communication signals over the wide spectral coverage range from 0 to 100 GHz. Nowadays, quantum sensing technology transforming numerous areas for the military sector, from delivering highly precise positioning information to discovering submarines in the world’s oceans, which is further expected to improve growth of market during the forecast period.
The quantum sensors market is segmented into the following categories:
By product type: atomic clocks, magnetic sensors, photosynthetically active radiation (PAR) quantum sensors, and gravity sensors.
By application: military and defense, automotive, healthcare, agriculture, oil and gas, and others.
By region: North America is segmented into the United States, Canada, and Mexico; Europe is segmented into the United Kingdom, Russia, Italy, Germany, and Rest of Europe; Asia-Pacific is segmented into China, Japan, India, and Rest of Asia-Pacific; Rest of the World (RoW) is segmented into Brazil, the Middle East, Africa, and Rest of RoW.
The atomic clocks segment is leading the global quantum sensors market and is estimated to exceed the market valuation of USD 120 milllion by the end of 2023. Sales of atomic clocks are being driven by new applications such as smart grids and “time stamping” in the financial services industry, as well as growth of private navigation systems outside of public GPS. There are also important technological changes in atomic clocks, notably the emergence of chip-scale devices
Numerous scientists working on quantum sensors have set up companies to commercialize their technology, but few have actual products on the market. One that does is Muquans, on the outskirts of Bordeaux, France. Set up by colleagues of Pereira Dos Santos at SYRTE, Muquans focuses on gravimeters made from atom interferometers, which exploit the quantum-mechanical property of wave-particle duality (see sidebar, below, and “Then and Now,” OPN, June 2019).
Some of these devices – such as PAR sensors – represent relatively mature technology. Others – gravity sensors and quantum LiDAR – are only beginning to make an impact. Kai Bongs, a physicist at Birmingham University, U.K., believes that gravity-measuring quantum sensors in particular “will become more widespread quite quickly,” with a potential market of perhaps US$1 billion a year.
Some of the end-user markets there will be the most significant opportunities including: Autonomous vehicles, navigation, GPS, air traffic control, agriculture, telecom, smart grids, construction, finance, healthcare, defense, aerospace, the Internet of Things and R&D.
AOSense, Radix, GWR Instruments Inc., Technology (Microsemi), Networking (Oscilloquartz), Spectrum Technologies Inc., METER Group, Adcon Telemetry Gmbh, Apogee Instrument Inc., Thomas Industrial Network Inc., Microchip, Impedans Ltd., M-Squared Lasers Limited, Skye Instruments Ltd., Biospherical Instruments Inc. and ADVA Optical.
Medical applications for quantum sensors will reach almost $270 million by 2023 as the result of a broad range of fast growing applications in medical imaging and medical wearables. Quantum imaging devices may be used to supplement existing medical imaging modalities and there will be a large growth in demand for SQUID sensors as the result of the growing number of applications for magnetoencephalography (MEG), which can be more comfortable than MRIs
The quantum sensors market will also provide significant opportunities in the future for specialty chemical companies and firms that sell novel materials in research quantities. For example, there is considerable materials development work around building new kinds of superconducting nanowire single-photon detectors (SNSPDs). Quantum dots, graphene, silicon and industrial diamond appear to also have important roles to play in the future of quantum sensors.
key players active in the global market, including AOSense, Apogee Instruments Inc., GWR Instruments Inc., Microsemi Corp., M Squared Laser Ltd., Sea-Bird Scientific and Skye Instruments Ltd.
Major Five Quantum Sensors Companies:
ADVA Optical Networking SE
ADVA Optical Networking SE offers quantum sensors through its subsidiary Oscilloquartz SA (Oscilloquartz). The company’s key offering include OSA 3230 Series, which is a cesium clock that offers precise timing for both next-generation networks and legacy infrastructures such as synchronous optical networking (SONET)/synchronous digital hierarchy (SDH).
AOSense Inc. has business operations under various segments, which include atom sources, electronics, sensors, and laser systems. The company offers Gravimeter, which is an accelerometer that is used to measure local gravity or variations in the gravitational field of the Earth.
Apogee Instruments Inc.
Apogee Instruments Inc. offers quantum sensors and meters that are used for PAR measurement, specifically in research and agricultural projects. The company’s key product offerings include Full-spectrum quantum sensor, which provides an accurate measurement of PAR from all light sources that are used to grow plants and corals.
GWR Instruments Inc.
GWR Instruments Inc. offers iGrav, a portable superconducting gravity meter specifically designed for geophysical applications that require much higher stability and precision than those provided by mechanical spring-type gravity meters.
Kipp & Zonen BV
Kipp & Zonen BV owns and operates businesses under various segments such as solar instruments, atmospheric science instruments, DustIQ soiling monitoring system, and RT1 smart rooftop monitoring system. The company’s key offerings include PQS1 PAR, a quantum sensor that offers the measurement of PAR with easy indoor and outdoor installation, ideally suited for studies of crop growth in greenhouses.