Google was the talk of the APS March Meeting on Monday, as Julian Kelly of the company’s Quantum AI Lab unveiled a 72-qubit quantum processor – the largest so far reported. The team hopes that the chip will allow them to achieve so-called quantum supremacy, the point at which a quantum computer can solve problems that are beyond the power of conventional devices.
The Google engineers are now starting to test the 72-qubit chip, which has been dubbed Bristlecone because its qubits are arranged in pinecone-like pattern. “From what we know so far, we’re very optimistic,” said John Martinis, a physicist at Google and the University of California Santa Barbara. If all goes well, Martinis is confident that quantum supremacy could be demonstrated with the next few months.
The Google announcement follows news in November that IBM Research was starting to test a 50-qubit quantum processor, while Intel revealed a 49-qubit test chip in January. But among these headline-grabbing announcements, James Wootton at the University of Basel – also speaking at the APS meeting – striked a note of caution.
Quantum games
Wootton has been creating simple games and puzzles to benchmark the performance of current prototypes, and his tests so far suggest that they still have a long way to go. “Devices now exist that are larger and cleaner than ever before,” he comments. “They’re on the cloud and they can be accessed using standard programming tools.”
Wootton’s approach stems from a long tradition of using games both to test computer hardware and to teach programming skills. And just as the hardware for quantum computing is only just starting to emerge from university labs and commercial companies, scientists also need to learn a new skill of quantum software engineering – in other words, how to use quantum processes to perform computations.
“When we start programming any sort of system we will first try something really simple,” says Wootton. “A game is a good place to start.”
To begin with Wootton created a version of the game Battleship, and used it to develop a tutorial to help scientists start programming quantum computers. He then moved on to another game, which he called Quantum Awesomeness, that tests the performance of a quantum processor with a series of increasingly difficult puzzles.
His results reveal that noise remains a major limiting factor for the current generation of prototypes, which typically have 16–19 qubits. “Based on tests with devices from IBM Research and Rigetti, even 50-qubit devices won’t be clean enough to achieve quantum supremacy,” he says. “The device size and connectivity determines the complexity of the device, while the noise levels determine how well the device can play the game.”
A new laser system that can make precise measurements of distance at record-breaking speed has been unveiled by researchers at Germany’s Karlsuhe Institute of Technology (KIT) and the Federal Institute of Technology in Lausanne (EPFL) in Switzerland. Made using optical frequency combs, the system can measure the surface profile of a speeding bullet.
Modern technologies such as aerial drones, observation satellites, self-driving cars and manufacturing robots need to make rapid, highly-accurate measurements of distances to surrounding objects. Currently, such measurements are made by laser-based light detection and ranging (LIDAR) systems, but even these are struggling to keep pace.
Optical teeth
To construct a faster ranging system, the KIT and EPFL scientists exploited solitons, which are wave packets consisting of laser light that maintain their shape as they propagate. These solitons can take the form of optical-frequency combs, with “teeth” of light with precisely defined wavelengths, spaced at regular intervals (see figure). The scientists realized that if one comb was fired at and reflected off a moving object, it would interfere with another, newly-produced comb. With knowledge of the comb structure, the phase difference of the superimposed teeth would reveal the distance travelled by the first comb.
To create the combs, the scientists fabricated circular, micron-scale pieces of high-quality silicon nitride, which loses very little light. When fed with continuous-wave lasers, the refractive index of this material responds to changes in electric field. Called the Kerr effect, this causes light waves at certain Kerr frequencies to resonate, producing the optical-frequency combs suitable for the team’s experiment.
“We have developed low-loss optical resonators, in which extremely high optical intensities can be generated – a prerequisite for soliton frequency combs,” explains Tobias Kippenberg of EPFL. “These so-called Kerr frequency combs have rapidly found their way into new applications over the previous years. “
Record breaking
To test their system, the researchers fired a bullet at a speed of 150 m/s and aimed a comb-producing laser perpendicular to its trajectory. By continuously observing comb interference patterns, they generated a 3D image of the bullet. “We managed to sample the surface structure of the projectile on-the-fly, achieving micrometre accuracy,” comments KIT’s Christian Koos. “To this end, we recorded 100 million distance values per second, corresponding to the fastest distance measurement so far demonstrated.”
While the measurement was made at both high precision and high speed, the range of the technique is only around 1 m – a value they wish to increase in the future. Additionally, their system is rather large and generates a huge amount of data. The researchers will now work towards producing a more compact design, which they believe could one day fit inside a matchbox.
Physicists in the US have cast doubt on a 2015 report that neutrons with orbital angular momentum (OAM) were created and characterized in the lab.
Ronald Cappelletti, Terrence Jach and John Vinson of the National Institute of Standards and Technology (NIST) in Gaithersburg Maryland have calculated that neutron interference effects measured by Dmitry Pushin and colleagues at the University of Waterloo, NIST’s Joint Quantum Institute in Maryland and Boston University are not related to neutron OAM.
Writing in Physical Review Letters, Cappelletti, Jach and Vinson also argue that the technique developed by Pushin’s team is extremely inefficient at creating neutrons with OAM.
Do the twist
Physicists know that particles such as photons and free electrons can have orbital angular momentum. This is a quantum-mechanical effect whereby the wavefront of the electron, for example, twists around its direction of propagation like a spiral of fusilli pasta.
Three years ago, Pushin and colleagues did an interferometry experiment that involved splitting a beam of slow-moving “cold” neutrons so that they travelled along two different paths. In one path they placed a spiral phase plate (SPP), which is a coin-sized piece of solid aluminium that resembles one twist of a spiral ramp. The other path was free of any objects. Neutrons travelling down the two paths were recombined and the quantum interference was measured. The neutron flux was set so low that the experiment was essentially measuring the interference between individual neutrons in a superposition of having taken the two different paths.
When a neutron travels through aluminium, its speed changes slightly. The spiral nature of the SPP and the fact that the neutron has a wavefront that extends over space mean that the shape of the wavefront changes as the neutron passes though the SPP. Pushin and colleagues argued that this imparted OAM to the neutrons – something that had already been seen for laser light passing through SPPs – and that evidence of neutron OAM was apparent in the resulting interference pattern.
Short on coherence
Cappelletti, Jach and Vinson have now, however, done calculations that they say show that the experiment actually measured phase-contrast interference, which has nothing to do with OAM. They point out that the neutrons used in the experiment had wavefronts that extend coherently about 5 µm in the direction transverse to their motion. This, the trio argues, is much too small relative to the size of the SPP for OAM to be imparted to the vast majority of neutrons passing through the apparatus. They point out that this size mismatch does not occur in SPP-laser experiments, where the coherence of the laser beam extends across the SPP.
The trio then went on to calculate that only about one in a million neutrons would acquire OAM in the 2015 experiment, which is too low to be measured. This number, they calculate, could however be boosted significantly if the neutron coherence length and the SPP were matched in size.
Production of butanol and hexanol may now be environmentally friendly thanks to a process that couples solar-powered electrochemical CO2 reduction and fermentation. Scientists from Siemens, Evonik and Covestro developed the hybrid system, which offers a sustainable, scalable, and efficient way to both reduce CO2 levels and produce value-added chemicals.
Alcohols like butanol and hexanol are widely used in coatings, solvents, cosmetics and fuels. Unfortunately, they are usually produced from depleting fossil sources using a costly and complex process, prompting Guenter Schmid and colleagues to design an alternative.
To drive alcohol production kinetically requires CO. The electrochemical cell in the researcher’s hybrid system uses a porous silver gas-diffusion electrode capable of uniquely high current densities (up to 300 mA cm–2), and an extended lifetime (up to 1200 hours) to produce syngas (CO/H2CO2 from CO2 and H2O, which the bioreactor then converts into valuable alcohols. High current densities are required to drive CO2 reduction at the electrolyser due to the low solubility of CO2 in salt-based electrolytes. The voltage required to drive CO2 reduction is provided by a commercial photovoltaic (PV). This solar cell provided up to 1200 hours of 70% CO-Faradaic efficiency Previously such high efficiencies have only been attained for a few minutes under these conditions or when very high CO2 pressures were used.
Thanks to the high-performance characteristics of the electrochemical cell, the system reached overall photon-to-alcohol efficiencies of 8%, making it one of the most efficient reported for oxygenate production from solar-driven CO2 hydrogenation.
Scaling up: CO2 electroreduction
The researchers also suggest how the process could be scaled up based on the reactions that take place. The cathode reduces CO2 to CO in a reaction that oxidizes water molecules into hydroxide anions (CO2+H2O+2e → CO+2OH–). The water oxidation takes place at the anode, which was composed of an iridium-oxide-coated platinum electrode: H2O-2e → 1/2O2+2H+. The alkaline cathode electrolyte requires an excess of CO2 for its neutralization: full reduction of one CO2 molecule requires three molecules of CO2 (3CO2+H2O+2e → CO+2HCO3-).
Overall, scaling up to produce 10,000 tonnes of hexanol and butanol requires 3.4 × 109 moles of electrons: the CO2 electrolyser provides 16.7% of these electrons, and the H2O electrolyser provides the rest. The plant would consume about 25.5 MW, which 14.6 hectare PV modules would supply. This amount of alcohol would also require 25,000 tonnes of CO2, which amounts to scaling up the CO2 electrolyser by a factor of 270,000, for instance by increasing its surface area of 10 cm2 to 1 m2 (factor 103) and by stacking 270 electrolysis cells.
Scaling up: fermentation
The bioreactor contained two anaerobic cultures, which bioprocessed the alcohols under non-growth conditions: C. autoethanogenum and C. kluyveri. Firstly, C. autoethanogenum transformed CO, H2 and CO2 to acetate and ethanol, which was then further inoculated by C. kluyveri to produce butanol and hexanol.
Scaling the fermentation to produce 10,000 tonnes of alcohols would require an increase in the number of fermenters (bacteria) by a factor of 21.6 × 106. The researchers calculated that increasing the cell concentration by a factor of up to 30 and the volume from 1 litre to 700,000 litres would achieve this. Even though the cultures must be placed in separate containers, these would only require vitamins and minerals for their media.
The hybrid system highlights the importance of research collaboration across diverse scientific fields that can lead to creative and efficient ways to decrease CO2 levels while producing highly desired chemicals. Furthermore, the modular and local alcohol production the research group proposes and the use of renewable energy paves the way to not only eco-friendly but also economically feasible systems for the generation of specialty chemicals.
Mexico City is one of the most populous cities in the world and it is facing a water crisis. Built on an ancient lakebed, the city’s geography leaves it vulnerable to a range of natural hazards, perhaps most notably earthquakes, as witnessed during the 2017 Central Mexico earthquake that claimed the lives of more than 200 people in Mexico City. The city’s soft underlying soils that amplify seismic waves are also causing the city to sink in places, which can damage water supply pipes causing leakages. Around 70% of Mexico City’s inhabitants receive tap water for just a few hours a day, instead relying on trucks to bring water to local storage tanks. Meanwhile, the city is also notoriously prone to flooding as water that would have filled natural wetlands is now forced over the vast urban sprawl.
This film investigates Mexico City’s troubled relationship with water. It takes viewers to one of the city’s only remaining chinampas – artificial islands originally created by the Aztecs who in the 14th century established a settlement on the site of current day Mexico City. These floating gardens provide a glimpse into the city’s origins and reveal the nature of the city’s silty foundations. The short documentary also explores some of the engineering and planning solutions to tackle these environmental challenges. At a local scale, residents are working with organizations to capture drinking water from rainfall. On a larger scale, there are transformational ideas such as restoring the ancient wetlands, or using geothermal energy from Popocatepetl volcano to pump water into the city from the Valley of Mexico.
This film is the first in a series of films we are producing about environmental challenges and the solutions being used to adapt to create more sustainable futures.
Cities built on a grid pattern, like New York and Chicago, build up more heat than those with a chaotic structure, such as Boston or London. That’s according to researchers from the US and France, who assessed the local urban heat island effect.
Urban building materials absorb heat during the day and radiate it at night, to a much greater extent than vegetation does. This, along with waste heat, creates a heat island effect that raises city temperatures above rural ones, particularly at night.
To come up with the result, the team looked at 47 city layouts from satellite images, using mathematical models designed to analyse atomic structures. Each city received a ranking for its local order parameter, which ranges from zero for total disorder to 1 for a perfect “crystalline” structure. The parameters for the cities varied from 0.5 to 0.9.
City structure appears to affect the heat island effect as buildings can reabsorb heat radiated out by buildings that are directly opposite them.
The findings could be useful for building new cities or expanding existing ones. “If you’re planning a new section of Phoenix,” said Roland Pellenq of MIT and France’s National Center for Scientific Research, “you don’t want to build on a grid, since it’s already a very hot place. But somewhere in Canada, a mayor may say no, we’ll choose to use the grid, to keep the city warmer.”
In the state of Florida, the team estimated, urban heat island effects cause around $400 million in excess costs for air conditioning. Although a grid pattern makes it easier to plan utility lines, sewer and water pipes, and transport systems, the heat savings from a less organised city structure could be worth the extra complications in hot areas.
Research on construction materials may also help manage heat interaction between buildings in cities’ historical downtown areas, according to the team.
Physicians and biomedical engineers at The Ohio State University are exploiting 3D printing technology to help select the optimal valve for a patient receiving an aortic valve replacement. Using CT scans to model the patient’s aorta, they create a 3D-printed replica and use this to predict potential complications – such as leaks, blockages or blood clots – so that they can be avoided.
There are currently two options available for replacing a diseased aortic valve: open heart surgery or a less invasive transcatheter method that deploys a bioprosthetic valve through a blood vessel in the leg. To decide which approach is best for each patient, the researchers create personalized 3D models of the aortic valve and neighbouring structures and investigate how the new valve will function.
“Using a simulator in a lab, we can replicate what happens in a patient’s left ventricle,” explained Prasad Dasi, a biomedical engineer at The Ohio State University College of Engineering. Dasi’s team precisely reconstruct a patient’s aorta and 3D print it using flexible materials that mimic the aorta. They load the model into a heart simulator that pumps transparent, simulated blood through the system, and then measure blood flow velocity and vortex patterns with and without a replacement valve.
“We can model various therapies, positions and types of valves to better understand problems such as leakage, clotting or coronary obstruction,” Dasi explained. “We can observe how different valves not only relieve the stenosis but also minimize the likelihood of blood clots forming, which is the goal of the treatment.”
At the same time, the team creates computer models to capture the physics of blood flow and interaction between the transcatheter valve and the patient’s anatomy. Long term, their goal is to understand each patient’s unique anatomy and blood flow without performing the physical model experiments, thus speeding the process of personalizing treatment decisions.
“We currently have two valves to choose from in the transcatheter world. I suspect we will have at least four within two years,” said Scott Lilly, interventional cardiologist at The Ohio State Wexner Medical Center. “Each valve is a little different, and the anatomy of every patient is unique. The ability to predict the function of the valve after placement, and which valve may work best with the least amount of leak and without impinging on adjacent structures, is critical.”
Scott Lilly reviews a scan of a patient’s heart
Lilly noted that having clinical and biomedical engineering faculty at the same table discussing individual patients makes their heart programme stronger. “In some cases, for example, the coronary arteries come adjacent to where the valve would be placed,” he explained. “Using 3D modelling we can determine whether or not to protect these blood vessels during deployment, or even whether to proceed with valve replacement at all. These discussions have directly informed how we approach many valve replacement procedures.”
Dasi and Lilly are presenting results from this work at the CRT interventional cardiology conference, held this week in Washington, DC.
Injuries to the lumbar spinal cord severely impair leg movement, or even cause complete paralysis. Epidural electrical stimulation has emerged as a promising approach to restore motor control, but for severe injuries, recovering movement also requires a serotonergic replacement therapy. With this aim, a research team headed up at EPFL in Switzerland is developing neural interfaces that deliver both electrical and chemical neuromodulation to the spinal cord.
These interfaces, called “e-dura”, integrate a silicone substrate, stretchable gold interconnects, soft electrodes and a fluidic microchannel (chemotrode). Unlike existing implants, these can be inserted below the dura mater – the membrane surrounding the spinal cord – allowing highly targeted drug delivery.
“E-dura has mechanical properties that are similar to those of the dura mater itself,” explained first author Marco Capogrosso. “Therefore, biomechanical compliance is greatly improved compared with classical stiffer electrodes. This allows the implants to gently ‘sit’ on top of the cord without significant damage to surrounding structures.”
This subdural placement should also increase the selectivity of electrical stimulation and reduce current thresholds. To date, however, these advantages have not been validated. Capogrosso and colleagues have now combined in silico, in vivo and behavioural experiments in rats to evaluate the advantages of subdural implants for restoring motion via electrochemical stimulation (J. Neural. Eng.15 026024).
In silico simulations
To compare the spread of currents between epidural and subdural implants, the researchers developed a computational model of the rat spinal cord that included detailed geometry of the spinal roots. They first estimated the 3D voltage distributions elicited by stimulation from electrical contacts placed within the epidural fat (above the dura mater) and within the cerebrospinal fluid (below the dura mater). Iso-potential curves penetrated deeper into the dorsal roots (which contain the nerves involved in muscle activation) with the subdural electrodes.
The e-dura implants
They then used these voltage distributions to simulate electrical stimulation, finding that subdural stimulation recruits spinal structures at lower currents than epidural stimulation. The model estimated that subdural stimulation reduces the activation threshold by 10–20% compared with epidural stimulation. This reduction is attributed to the proximity of subdural electrodes to the targeted neural structures.
In vivo studies
Next, Capogrosso and colleagues validated the model in rats, using the same implant to deliver epidural and subdural spinal cord stimulation. In five rats, the electrode was first placed above the dura mater to perform epidural stimulation, then the dura mater was opened and the device was inserted below. The researchers delivered electrical pulses at increasing currents until motor responses recorded in leg muscles reached saturation.
In vivo recruitment properties of the subdural implants
Subdural and epidural electrical stimulation both achieved a graded recruitment of the distal leg muscles. Confirming the model’s predictions, subdural stimulation showed an average 15% reduction in current threshold compared with epidural stimulation. Stimulation delivered from the subdural and epidural surfaces achieved comparable, high levels of specificity, allowing side-specific recruitment of leg muscles.
The subdural implant’s ability to decrease stimulation thresholds while retaining high specificity reduces power consumption and risks of long-term damage in the tissues, increasing the clinical safety profile of this approach. The researchers confirmed the stability and safety of the implants in three rats, showing that the electrode threshold and impedance were stable over five weeks. Post-mortem assessment revealed that the implants did not damage the spinal tissue.
Restoring motion after injury
Finally, the team tested the ability of subdural implants to deliver electrochemical neuromodulation therapies. They inserted an implant with seven electrodes and a chemotrode below the dura mater of lumbar segments in six rats. The rats subsequently received a lateral hemisection of the spinal cord. In the weeks after this injury, all rats exhibited complete paralysis of the leg on the injured side, while the other leg could still produce movement when the animals were placed over a treadmill (attached to a body support).
For each test session, the researchers first delivered serotonergic therapy through the chemotrode, and then applied electrical stimulation to the rat’s injured side. This electrochemical neuromodulation restored weight-bearing locomotion of the paralyzed leg in all rats, without affecting the intact leg.
This ability to deliver chemical and electrical neuromodulation simultaneously via a single implant is of great value for clinical translation. “Right now, systemic delivery of drugs would significantly affect the behaviour and mood of patients,” Capogrosso explained. “To allow safe delivery of a sufficient amount of drug to the spinal circuits, we think that local drug delivery is a viable solution. This may be the only option for people suffering from severe motor paralysis to be able to efficiently use electrical stimulation of the spinal cord to recover motor function.”
Next, the researchers aim to demonstrate that spinal cord stimulation is as effective in humans as it is in rats, using classical stiffer epidural interfaces. “If this is the case, all the work that we performed in rats and primates can be translated to clinical settings, including subdural interfaces,” said Capogrosso. “However, e-dura is still an experimental device and significant work needs to be done to scale this technology to human applications.”
By the end of this century the number of people exposed to heat-wave conditions in India is likely to multiply between 18 and 200 times, depending on which climate path the world follows. More than 20,000 people have died from heat-related causes in the nation since 1990.
Heat waves are the most lethal weather phenomenon in the world. For example, the 2003 heat wave across Europe is estimated to have killed more than 70,000 people; significantly more than even the most major floods, hurricanes and tornadoes. As our planet continues to warm, heat waves are expected to occur more frequently and to last for longer.
In India the increase in number and duration of heat waves is already evident, with a clear rise in dangerous heat waves in recent years. The five most severe of the top-ten heat waves since 1951 occurred after 1990.
Previous work has investigated how heat-wave frequency and duration might increase in the future across India, but until now little had been done to assess the impact on population exposure. It isn’t always the hottest heat waves that pack the biggest punch. In the 2015 event an estimated 2500 people died from heat-related causes, making it India’s second most deadly heat wave. However, this heat wave failed to be classified in the top ten because it was localized over the east of the country.
Vimal Mishra from the Indian Institute of Technology (IIT) Gandhinagar and his colleagues combined climate models with population scenarios for India to investigate how many people might be exposed to heat waves across India in the future. Climate models project that the frequency of severe heat waves in India will increase 30-fold by the end of the century under a 2 °C warming scenario. Under a business-as-usual scenario (RCP 8.5) heat-wave frequency increases 75-fold.
“Heat waves like 1998 [where more than 2000 people died] are projected to occur every year in the late 21st century under a business-as-usual scenario,” said Mishra.
By looking at the number of days that heat waves were expected to last, and the estimates of population increase, the researchers estimated the number of people likely to be exposed to heat waves each year, and totted up the number of days that they were likely to be exposed.
The results show that population exposure to heat waves is expected to increase by around 18-fold by the end of the century under a 1.5 °C warming scenario, 92-fold under a 2 °C warming scenario, and a massive 200-fold under business-as-usual warming.
When it comes to mitigating for heat-wave exposure, the researchers note that strategies to reduce population growth in India during the 21st century may not reduce exposure to heat waves as much as hoped.
“The heat-wave exposure is dominated by the increase in length of heat waves, rather than population increase,” they said. Instead, the largest mitigation effects are seen by reducing greenhouse-gas emissions. “We show that low-warming scenarios can provide substantial benefits in reducing the frequency of severe heat waves in India. Limiting global temperatures to 1.5 °C would reduce exposure by half by the mid-21st century, compared to business-as-usual,” Mishra added.
In the meantime, whichever climate scenario unfolds, India is going to have to look at serious adaptation measures such as increased provision of shelter, more cooling systems, modification of daily behaviour patterns and developing emergency public services to cope with heat-wave associated problems. But reducing global temperature will be key.
“Slowing the rate of global warming would provide vital time for further development of measures to reduce actual exposure,” writes the team in Environmental Research Letters (ERL).
Sarah Tesh and Susan Curtis are reporting from the APS March Meeting in Los Angeles, California
While the stars of stage and screen were preparing themselves for the Oscars on Sunday, Sarah and I visited an iconic location that has taken a starring role in such films as La La Land and Rebel Without A Cause. Set on a hill a few miles from downtown Los Angeles, the Griffith Observatory has been open to the public since 1935, offering visitors a close-up view of both the stars in the night sky and the very special one at the centre of our solar system.
As we found out, the observatory is a popular destination for Angelinos on sunny Sunday afternoon. It offers majestic views of the city below, the ocean in the distance, and even the famous “Hollywood” sign – which is situated on another hill in the surrounding Griffith Park. But the main attraction is the observatory itself, complete with a state-of-the-art planetarium, a telescope that opens for public viewings, and a ceolostat that allows visitors to see a filtered image of the Sun.
The idea for a public observatory emanated from the imaginatively named Griffith J Griffith, a Welshman who had moved to California to make his fortune from silver mining. Griffith was inspired by the emerging field of astronomy, and in particular the breakthrough discoveries that had been made by Edwin Hubble and other pioneers at the Mount Wilson Observatory, located in the mountains to the north-east of Los Angeles. He made a bequest in his will to the city, specifying that it should be used for the construction of an observatory that would allow ordinary people to see the wonders of the solar system for themselves.
Today, the observatory houses innovative exhibits that explain how the Sun, Earth and Moon interact to create phenomenon such as the seasons, the tides, and solar and lunar eclipses. There are plenty of buttons to press, eyepieces to look through, and well-conceived demonstrations of more complex concepts such as adaptive optics and solar spectroscopy.
One of my favourite spaces was the central rotunda, which is decorated with murals representing some of key ideas in astronomy and featuring a huge Foucault pendulum that demonstrates to visitors that the Earth is rotating beneath them. But the observatory provides plenty of other opportunities for the visiting public to see how telescopes are used by astronomers to reveal the secrets of the cosmos, and in particular to study the most important star to everyone here on planet Earth.
