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Quantum squeezing boosts performance of LIGO and Virgo gravitational-wave detectors

Quantum squeezing has been used to increase the sensitivity of the LIGO and Virgo interferometers, making them better at detecting gravitational waves. The technique involves reducing the inherent uncertainty in the time at which photons arrive at detectors after travelling on round trips of several kilometres along the interferometer arms. Squeezing was implemented in April 2019 and has boosted the sensitivity of LIGO and Virgo detectors by factors of 20% and 50% respectively.

Since 2015 the two LIGO interferometers in the US – and more recently, the Virgo interferometer in Italy – have been detecting gravitational waves (ripples in spacetime) from merging pairs of black holes and neutron stars.

Each detector comprises two perpendicular interferometer arms, which are 4 km long at LIGO and 3 km at Virgo. An interferometer works by splitting laser light into two beams that travel out along the arms. The beams bounce off mirrors at the ends of the arms and return along the arms to their vertex, where the light is recombined and detected.

Subatomic-sized changes

The LIGO and Virgo interferometers are set so that the light undergoes destructive interference at the detector, which normally measures a null signal. When a gravitational wave moves through the interferometer it can cause tiny changes in the length of one or both arms. Destructive interference no longer occurs, and some light is detected. In this way, the detectors are able to measure length changes as small as 10⁻¹⁹m – which is about 10,000 times smaller than the diameter of a proton.

An important limitation on the precision of these measurements is noise caused by quantum fluctuations in the light. These fluctuations create a small spread in the times that it takes photons to travel back and forth along the arms of an interferometer. As a result, the destructive interference at the detector is not perfect and the ability of the interferometer to measure a change in arm distance is limited by the width of the distribution of the arrival times of the photons.

Fortunately, quantum mechanics offers a way of reducing the time-distribution width. The “radiation pressure” exerted by the light on optical components within the interferometers also undergoes quantum fluctuations. The uncertainty principle dictates that the product of the time and radiation-pressure distribution widths must be larger than a certain value. It is possible, therefore, to reduce the width of the time distribution at the expense of increasing the width of the radiation-pressure distribution.

Entangled pairs

In both the LIGO and Virgo detectors, the time distribution width has been reduced – or squeezed – by creating pairs of photons using a special device called an optical parametric oscillator. The pairs are quantum-mechanically entangled and have correlated arrival times at the detector – thus reducing the width of the time distribution.

A wave of discovery

Thanks to squeezing, LIGO can now observe astronomical sources of gravitational waves that are about 15% more distant than before – which means that LIGO should be able to spot 50% more objects. Virgo can now see objects that are up to 8% further away, which should allow it to see about 20% more objects.

However, the nature of the uncertainly principle means that LIGO and Virgo physicists must accept greater radiation pressure noise – which tends to degrade the performance of the gravitational wave detectors. This is much more of a problem when trying to detect low frequency signals (below about 50 Hz in LIGO) and is not currently considered a problem for the detection of neutron star and black-hole mergers.

Separate papers in Physical Review Letters describe squeezing in the LIGO and Virgo detectors.

A decade of Physics World breakthroughs: 2015 – double quantum-teleportation milestone

In October 2013, Physics World celebrated its 25th anniversary. As part of our special issue, we picked five of the biggest and most significant discoveries in fundamental physics, made over the previous quarter century – one of which was quantum teleportation. It was no surprise then, that only two years later, our 2015 Breakthrough of the Year went to Jian-Wei Pan and Chaoyang Lu of the University of Science and Technology of China in Hefei, for being the first to achieve the simultaneous quantum teleportation of two inherent properties of a fundamental particle – the photon.

Teleportation has long been the stuff of fantasy and sci-fi, but science eventually caught up with fiction in 1993 when an international group of scientists said that quantum teleportation – the instantaneous transfer of a state between particles separated by a long distance – is entirely possible, so long as the original state is destroyed (thanks to the “no-cloning” theorem).

In the basic quantum teleportation protocol, an observer, Alice, sends information about an unknown quantum state to another observer, Bob, by exchanging classical information. To do this, a “quantum channel” must exist between the pair, which is created by giving both Alice and Bob are one half of an additional pair of entangled particles. Alice then interacts the unknown quantum state with her half of the entangled particle and measures the combined quantum state, before sending the result through a classical channel to Bob. The act of the measurement itself has already altered the state of Bob’s half of the entangled pair and this, combined with the result of Alice’s measurement, allows Bob to reconstruct the unknown quantum state, with no copies, and with the entanglement secure.

The first experimentation teleportation of the spin (or polarization) of a photon took place in 1997, and Pan was a part of this seminal research team, then under the tutelage Anton Zeilinger, his former PhD supervisor at the University of Vienna. Since their ground-breaking experiment, a whole host of various quantum proprieties, including atomic spin-states, nuclear spins, trapped ions and coherent light fields have all been teleported.

But all quantum particles (even simple ones such as the photon or the hydrogen atom) possess more than one inherent property or state (“multiple degrees of freedom”). So being able to teleport more than on of these at the same time would be a key step forward for any quantum communication protocol. Pan and colleagues’ 2015 award-winning experiment achieved precisely this, as they showed that they could reliably and repeatedly teleport a photon’s spin (polarization) and its orbital angular momentum (OAM) to another photon some distance away, at the same time. Their quantum channel in their protocol included a “hyper-entangled” set, where the two particles are simultaneously entangled in both their spin and their OAM.

There is an upper limit of three properties for this particular protocol, and Pan had told Physics World in 2015 that to achieve even that was a herculean feat as it requires the experimental ability to control 10 photons. “So far, our record is eight photon entanglement. We are currently working on two parallel lines to get more photon entanglement.”

Since then, Pan, Lu and colleagues have been rather busy with a whole host of amazing quantum feats, including launching the world’s first quantum satellite (2016) which exchanged quantum information between China and Austria; carrying out a teleportation experiment over 10kms in Hefei (2016); and even transmitting quantum data (to recreate an image) without the exchange of any particles (2017, this work featured on the Top 10 list of our 2017 Breakthroughs). Earlier this year, Pan and Lu’s team even showed that they can teleport multi-dimensional photon states (going beyond the 2D subspace of a qubit) – a follow-on to the 2015 work. The team reported the first quantum teleportation of what they call a qutrit, taking teleportation into 3D, a key step towards teleporting the entire quantum state of a particle. As Lu told Physics World, their scheme could be easily scaled up to go to four, five or more dimensions. Their team is now working on combining these higher dimensions with the multiple degrees of freedom, to try teleport complete particles.

You probably won’t be surprised to hear that Time magazine named Pan as one of its 100 Most Influential People of 2018 . Pan’s long-term goal is to set up a global quantum Internet, and at this rate, it won’t be that long before that too becomes a reality.

Portable RFG gel scanner rapidly creates 3D images of radiation fields

FluoroTome 1 is a portable apparatus that performs on-site tomographic scanning of radio-fluorogenic gels within minutes of radiation exposure. (Courtesy: CC BY 4.0/J M Warman *et al Polymers* 10.3390/polym11111729)

The ability to create 3D images of radio-fluorogenic (RFG) gels following radiation exposure could enable visualization of the dose deposited during a radiation treatment. To achieve this, researchers in the Netherlands have created a portable, user-friendly device – called FluoroTome 1 – that can rapidly read out an irradiated gel to produce a series of fluorescence images (Polymers 10.3390/polym11111729).

RFG gels become permanently fluorescent when exposed to high-energy photon or particle radiation, with the emission intensity proportional to the local absorbed dose. One important application of this property is use in high-resolution radiotherapy dosimetry. FluoroTome 1, developed by John Warman and researchers at TU Delft, enables on-site scanning of RFG gels, creating multiple tomographic slices of the fluorescence signal.

“Scanning of irradiated samples and data analysis can be carried out, using user-friendly software, within minutes of radiation exposure,” Warman explains. “This possibility of rapid, on-site feedback is particularly important for equipment testing, protocol control and educational applications, and is a feature that is not generally possible with other polymer-gel dosimetry equipment.”

Originally developed as a bench-top system, the new device is compact, portable and apart from two 220 V outlets, requires no special on-site facilities or a dark room. FluoroTome 1 was constructed in collaboration with Netherlands-based 4PICO BV, a firm with expertise in fabricating functional UV-optical devices.

FluoroTome 1 works by creating a thin sheet of uniform UV light, transporting the irradiated RFG gels through this sheet using a remotely controlled translation stage, and creating multiple digital images of the UV-excited fluorescence. The team successfully tested the FluoroTome 1 by using it to record images of a 20 x 20 mm square RFG gel irradiated with four 3 mm square 300 kVp X-ray beams.

FluoroTome 1 images of an RFG gel irradiated with four square X-ray beams. (Courtesy: CC BY 4.0/J M Warman *et al Polymers* 10.3390/polym11111729)

The system can also easily compile the recorded images into a 3D video of radiation dose deposition, enabling dosimetric verification of complex radiation fields.

Warman notes that FluoroTome 1 was specifically designed for application in collaboration with other radiotherapy or radiation physics groups. The portability of the apparatus, as well as its independence of special on-site facilities and user-friendly software, should enable it to be used in most high-energy radiation facilities. “The actual irradiation set-ups and specific gel containers used will of course need to be designed and constructed separately,” he notes.

The team’s immediate plans are to use FluoroTome 1 to monitor proton beams at the Holland Proton Therapy Centre, recently constructed on the grounds of TU Delft. “My own particular interest is in the fundamentals of radiation interactions with materials,” Warman tells Physics World. “These include problems such as the differences between chemical, physical and computational estimates of energy deposition in proton beams and the relative biological effectiveness at the Bragg peak. The application of proton pencil beams to ocular cancers is another interesting practical problem for which we recently performed preparatory measurements using a 3 mm X-ray beam and a gel phantom.”

More general applications of RBG gel studies include quality control testing of radiotherapy equipment and computer protocols. “The FluoroTome 1 could also become a fast-feedback teaching aid for students and clinical personnel. And, it could provide visual images for radiation oncologists to explain to patients the differences between different types of radiotherapy procedures.” Warman adds.

A relative journey

A trope that has indelibly attached itself to Albert Einstein’s theory of relativity, since its public debut, is that few individuals – save the great physicist himself – are fully able to grasp the science, despite it attracting interest from all quarters. In May 1931, for example, on the occasion of Einstein’s delivery of the Rhodes lectures in Oxford, UK, a local newspaper reporter commented: “It was unfortunate that no interpreter was provided…One wonders how many of those who were present thoroughly understood German, or if they could…how many of them could follow the complexities of relativity.” Indeed, in November 1919 astronomer Arthur Eddington – presented with the suggestion that he must be one of only three individuals in the world to understand general relativity – himself responded wittily that he was hard pushed to “think who the third person is”.

Reading his new book, Einstein on the Run: How Britain Saved the World’s Greatest Scientist, one cannot help but feel that author Andrew Robinson’s panoptic grasp of his world-renowned subject – on whom he has written previously – has by coincidence taken on a somewhat similarly formidable but irresistible appeal.

Robinson, who is also author of Einstein: a Hundred Years of Relativity, has that rare knack for presenting a near-encyclopedic volume of historical information, anecdotes and contemporaneous accounts in a thoroughly delightful fashion. Starting with Einstein’s upbringing in Germany, the book progresses through his presentation of the theory of relativity, to his flight to Belgium, England and eventually the US – weaving along the way a multi-stranded narrative about Einstein’s physics, changing relationship to pacifism, and political circumstances, with a particular focus on his relationship with Britain.

Einstein made a number of trips to England during the period from 1921 to 1933, and his speeches and writings from that time relate a not-inconsiderable affection for the country, the reception it had provided him, and its place in the history of physics – despite his amusement with aspects of English formality such as he observed in the University of Oxford’s “holy brotherhood in tails”.

I was particularly delighted by Robinson’s inclusion of various humorous reference materials from the time. These range from the writings of the pseudonymous Daily Express columnist “Beachcomber” to a relativity-themed rewrite of Lewis Carroll’s “The Walrus and the Carpenter”, and even the following amusing aphorism from writer Sir John Squire, after a poem by Alexander Pope:

“Nature, and Nature’s laws lay hid in night. / God said, Let Newton be! and all was light. / It did not last: the Devil howling ‘Ho! / Let Einstein be!’ restored the status quo.”

Perhaps one of the few criticisms I could level at Einstein on the Run manifests not through the body of the text, but the subtitle, which places the work as a telling of “How Britain saved the world’s greatest scientist”. My fears that this label pointed towards a more parochial take on the physicist were, fortunately, not realized. Instead, one might argue that the work stands as a subtle testament to the values of tolerance, co-operation and internationalism exhibited by many of the book’s key actors – which makes the work feel particularly timely.

Besides the scientific and political contexts of Einstein’s life, however, Robinson’s writing beautifully invokes the free-spirited professor’s playful personality, charm and good humour – rendering the man an endearing subject. Repeated references are made to Einstein’s kindly nature and booming laughter that would, in the words of the British literary critic V S Pritchett, blow away the “exemplary and decorous” atmosphere at Princeton’s Institute for Advanced Study.

Robinson contextualizes Einstein’s character and noted anti-authoritarian streak as a reaction against what he referred to as Zwang – the German word for constraint and compulsion – which he saw as a prevalent negative in the disciplined ethos of his upbringing in Germany. In contrast, the description of the provisions made for Einstein’s protection during his “secret” stay near Cromer, Norfolk, in 1933 capture a quintessentially British scene of quirkiness – with the great mind secured against Nazi assassins and other sinister actors by a gamekeeper, two “beautiful” rifle-bearing secretaries and a former naval officer sat astride a hired milk-cart pony named “Tom”.

In many ways, and quite belying its more active title, Einstein on the Run is a slow burner of a book – the lion’s share of its content passes before it even reaches his flight from the growing Nazi menace that threatened him. The work might almost be viewed as an extensive preamble to the tightly written final chapter, which addresses the question “Why did Einstein choose not to remain in England?”. For many authors, this structure would be fatal, but Robinson’s superb work remains compelling throughout. Whether or not one has successfully plumbed the depths of relativity, the certainty that this work has something for everyone is surely absolute.

2019 Yale University Press £16.99hb 376pp

Bragg diffraction monitors wound healing, plastic soil and other physical science innovations

Wound dressing — Smart wound dressing: Ruchi Gupta holds a model of her optical biosensor. (Courtesy: Hamish Johnston)

On Friday I was at the Institute of Physics (IOP) in London for an event called “Showcasing Physical Sciences Impact”, which was organized by the UK’s Engineering and Physical Sciences Research Council (EPSRC), United Kingdom Research and Innovation (UKRI) and sponsored jointly by the IOP and the Royal Society of Chemistry.

There were a range of speakers from funding agencies such as UKRI, academia and industry, who talked about the far-reaching and varied impacts of physical sciences research.

I was particularly intrigued by a talk by the University of Sheffield chemist Tony Ryan, who goes by the moniker “Professor Plastic”. He spoke about his work on recycling and reusing plastics, including schemes for making plastic soils that can be used to grow plants in desert environments.

There was also a small exhibition of research projects from UK universities and I enjoyed having a chat with some of the exhibitors. Pictured above is Ruchi Gupta, who is a chemist at the University of Birmingham. Her research group has developed an optical biosensor that can be embedded in a wound dressing, and Gupta is holding a model of the layered structure.

Bragg reflector

Normally when a chronic wound such as a diabetic ulcer is dressed it cannot be inspected without removing the dressing – which can be painful and disrupt the healing process. Gupta’s biosensor allows doctors to determine whether a wound has become infected by revealing the presence of biomolecules that are associated with infection. This is done by embedding antibodies (shown in turquoise in the photo) in alternating layers of optical materials that form a Bragg reflector – which converts white light to monochromatic light of a certain colour.

When the biomolecules of interest bind to the antibodies, they change the colour of the reflected light – thereby revealing infection. As well as applications in healthcare, the technology could also be used other areas such as food security and environmental monitoring by using antibodies that capture different types of molecules.

Sussex ion qubits — Modular microwave: Sebastian Weidt with a larger-than-life model of an ion-based quantum computer. (Courtesy: Hamish Johnston)

I also had a chat with the physics Sebastian Weidt of the University of Sussex, who was exhibiting the “Sussex modular microwave ion quantum computer”. The device uses trapped ions as quantum bits (qubits), which are entangled and processed using microwaves. This, according to Weidt, offers a solution to the problem of scaling-up ion-based quantum computers, which would normally require impractically large numbers of laser beams.

Alice and Bob in a box — Box clever: Catherine Phillips with an optical demonstration of quantum encryption. (Courtesy: Hamish Johnston)

Staying on the theme of quantum information, I also met Catherine Phillips at the University of Sheffield who had Alice, Bob and Eve in a plastic box. More precisely, she had a demonstration of how the principles of quantum mechanics could be used to prevent eavesdropper Eve from listening-in on a conversation between Alice and Bob.

Trapped nanoparticles — Caught in a trapped: these nanoparticles could be used as interial sensors. (Courtesy: Hamish Johnston).

In the above photo you can just make out several optically-levitated nanoparticles that are being held by green laser light in the middle of the cube-like structure at the centre of the image. This demonstration belongs to James Millen of King’s College London, who is developing ways of using trapped nano-objects as inertial sensors. As well as being sensitive to linear accelerations, trapped nanoparticles can also be made to rotate and could therefore be useful in detecting angular accelerations.

Hot air — Speed of sound: Michael de Podesta demonstrates his new thermometer. (Courtesy: Hamish Johnston)

I just put on a jumper because I thought the office was getting a bit chilly, but then when I looked at a nearby thermometer it registered a balmy 25 °C. Perhaps we should invest in a new type of thermometer that has been developed by Michael de Podesta and colleagues at the UK’s National Physical Laboratory. That’s de Podesta in the above photo, blowing warm air into the device, which works out the temperature by measuring the speed of sound through the column of air between the two discs. If you look at the red plot on the laptop you can see a sudden jump in the temperature as his breath enters the column.

The physics-based firm that helped spawn the IVF revolution

In vitro fertilisation — World-changing: One application of Research Instruments’ micro-manipulators was in the creation of “test-tube” babies. (Courtesy: Mehau Kulyk/Science Photo Library)

Like many successful companies, Research Instruments (RI) got its start when its founders grew bored with their day jobs. It was the early 1960s, and Mike Lee and Vince Grispo began building prototypes in Mike’s attic. Their first instruments were micro-manipulators, which mechanically reduced and stabilized the movement of the hand so the person could carry out fine work under a microscope. In 1962 RI moved out of the attic and into a shed at the bottom of Mike’s garden, which they filled with a milling machine, a pillar drill, and some very good sound insulation to avoid annoying the neighbours or Mike’s wife, Ann Lee (née Lucas), who was working on RI’s sales and marketing.

In RI’s early years, the principal use for micro-manipulators lay in testing semiconductor integrated circuits. To measure a circuit’s response, testers had to make non-destructive connections to the fine wires linking individual components within the circuit. In 1970 these interconnection lines were about 30 microns across, half the diameter of a human hair. However, as the number of components per unit area increased, the lines grew narrower still. It soon became clear to Mike that RI needed either to find new applications for its micro-manipulators, or else diversify into other areas.

Mike had always worked closely with customers in research, and one of these collaborations led him to develop a new instrument. RI’s “ultrastage” could measure the alignment of an optical fibre to a fraction of a micron, and it was built on the specifications of a certain Charles Kao, who was then developing fibres for optical communications. Kao, of course, went on to receive a Nobel prize and a knighthood for his work, and he is now considered the “father of optical cables”. Solving a problem for this esteemed customer enabled RI to enter the growing market for R&D equipment for optics and photonics research.

Solving a problem for this esteemed customer enabled RI to enter the growing market for R&D equipment for optics and photonics research

By the late 1960s, RI had outgrown both Mike’s shed and a small industrial unit in London. A regional development grant helped the firm relocate to Penryn in Cornwall, where Mike, Vince, Ann and the employees settled into a custom-built space that cost the same as their old London premises, but was five times the size. During this period, the company continued to innovate and move with the times. One product, the “groovac”, was designed to suck away dirt from the grooves in vinyl records, improving their sound quality. It sold in large volumes until 1983, when declining record sales led RI to cease production.

Another variant of the micromanipulator product with integral micropipettes had a more long-lasting impact. One of its main applications was in fertility clinics, which sprang up after Robert Edwards, Patrick Steptoe and Jean Purdy developed in vitro fertilization (IVF) in 1977. Their technique involved mixing sperm and eggs together in a test-tube or culture dish, allowing the resulting fertilized eggs to grow, and then transferring them into the uterus.

Simon Fishel – a British biochemist and virologist – noticed the company at a trade show in Italy and worked with RI to develop its technology for fertility treatment applications. Fishel was a member of the team that produced the world’s first IVF baby, Louise Brown, who was born in 1978, and Edwards went on to receive the Nobel Prize for Physiology or Medicine in 2010. By that time, Mike and Ann had retired. RI continues to operate today as a division of a larger medical-equipment company (CooperSurgical Fertility and Genomic Solutions).

At this point, I can hear you saying, “That’s all very inspiring, James, but why are you writing about it?” Well, last year, I and my colleagues at the Institute of Physics (IOP) decided to add a new “start-up” category to the IOP’s Business Innovation Awards, which honour firms that built success on the innovative application of physics. As I explained in this column last year, early-stage companies had found it hard to provide enough evidence of commercial growth to qualify for the main Business Innovation Awards, but their work is nonetheless worthy of recognition. Early-stage awards, like the IOP’s, can raise a firm’s profile, lend credibility to a novel technology and generate constructive feedback from seasoned business leaders on the judging panel.

If there’s anything an early-stage business needs (apart from publicity and credibility), it’s cash

When Mike saw this column, he did something amazing: he wrote to me to say that he would like to add a cash prize to the IOP’s start-up awards. This got my attention right away, because if there’s anything an early-stage business needs (apart from publicity and credibility), it’s cash. After some discussions, I am pleased to say that the new Lee–Lucas Prize for early-stage businesses in (principally) medical physics will be awarded for the first time in 2020. The emphasis on medical physics reflects Mike and Ann’s wishes and the importance of such businesses to society but also that medical-physics businesses often take a while to get established these days – and thus need extra support mostly due to the challenging regulatory requirements associated with medical applications.

Endowing this prize is an extremely generous thing to do, and one that I am sure its recipients will appreciate. I also hope that Mike publishes his memoirs, so you can all read in more detail about how he and Ann created RI and grew it into a successful business. Theirs is a fascinating story of innovation, solid leadership and entrepreneurial determination, and I hope it will inspire other physicists to start companies and (of course) enter them in the IOP Business Awards. The closing date for next year’s awards is 3 January 2020. And if any other readers would like to write to me about sponsoring a prize, all I can say is: my inbox is open.

A decade of Physics World breakthroughs: 2014 – landing a spacecraft on a comet

Landing stuff on other worlds is hard. Just ask the people behind the Vikram lunar lander, which crashed onto the Moon in September 2019; or the Beresheet lunar lander, which met a similar fate in April; or the Mars Polar Lander, or the Beagle 2, or – well, you get the picture.

So when a little craft called Philae descended towards the comet 67P/Churyumov–Gerasimenko, touched down briefly, bounced off the surface, landed, bounced again, and finally came to rest on this 4.1km by 4.3km chunk of interplanetary ice, we thought it was quite an accomplishment. A month later, the ESA team behind the Philae lander and its parent Rosetta mission won Physics World’s 2014 “Breakthrough of the Year” for making the first non-destructive landing of a spacecraft on a comet nucleus.

In hindsight, Philae’s survival was something of a lucky accident. The harpoon that was meant to secure it to 67P/Churyumov–Gerasimenko failed to fire. A set of thrusters designed to push it onto the comet didn’t work either. And when the craft finally came to rest, it was in an awkward location, stuck on its side in a dark crevice that prevented its solar panels from functioning and made communication a challenge.

Fortune favours the well-prepared, though, and the ESA team made the most of Philae’s 57-hour operational life, gathering reams of scientific data from a suite of onboard instruments before the probe’s batteries failed. Among other achievements, Philae sniffed out organic molecules on the comet’s surface and discovered that the material in its immediate vicinity was much harder than expected. Studies of the comet’s deuterium-to-hydrogen ratio also lent support to the theory that asteroids, rather than comets, brought water to Earth – an important contribution to our understanding of the early solar system.

Missions like Rosetta don’t come along very often, so it’s not surprising that no-one else has landed on a comet since 2014 (or tried to). But the success of ESA’s lander fired imaginations and fuelled an interest in the solar system’s smaller objects that continues today. Just last week, NASA’s OSIRIS-REx mission announced a series of discoveries about particle ejections from an asteroid called Bennu. Over the summer, another spacecraft, Hayabusa-2, scooped up samples from the asteroid 162173 Ryugu. Hayabusa-2’s samples are now on their way back to Earth, and towards the end of 2020, scientists at JAXA, the Japanese space agency, will have their own nerve-wracking moment when they attempt to retrieve them.

Perhaps the most intriguing development in this field came in October 2017 with the unexpected arrival of a small, irregularly-shaped object known as ‘Oumuamua. Initially designated as a comet, and later reclassed as an asteroid, ‘Oumuamua is now thought to be neither. Instead, it is an interstellar visitor – the name ‘Oumuamua means “scout” in Hawaiian – and its exact composition is a matter of much scientific debate (as well as endless science-fiction-driven speculation). A craft like Philae or Hayabusa could answer those questions, and a group of scientists at a non-profit organization, the Institute for Interstellar Studies (IIS), has duly proposed a rendezvous mission to ‘Oumuamua.

Most space missions take a while to get off the ground, and with ‘Oumuamua already on its way out of the solar system, the odds seem stacked against the IIS scientists. But other, similar missions are also under development. One of them, ESA’s Comet Interceptor, is designed to visit a comet or interstellar visitor that hasn’t even been discovered yet. According to Geraint Jones, a planetary scientist at University College London and co-leader of the team that proposed the mission, the idea is to place the spacecraft in a dynamically-stable location (the L2 Lagrange point of the Earth-Sun system), wait until a suitable object comes along, then send the craft to investigate it. Something like ‘Oumuamua would be ideal, but a long-period comet full of relatively pristine “leftovers” from when the planets formed would also tell us much about the early history of our solar system.

The launch date for Comet Interceptor isn’t until 2028, so it’ll be a while before we can enjoy a sequel to the comet-exploring achievements of 2014. As Philae and the Rosetta mission showed, though, some things are worth the wait.

Scientists find a simple solution for making ferroelectric nylon thin films

An efficient way of making ferroelectric nylon has been developed by Saleem Anwar and collaborators at the Max Planck Institute for Polymer Research in Mainz, Germany. The technique provides a starting point for the cost-efficient production of ferroelectric nylon thin films using commercially-available materials. Such films could find a wide range of applications including robotics, biomedical devices and energy harvesting.

We are all familiar with nylon as a synthetic material used for clothing, but some types of nylon have much more sophisticated applications. Nylon is composed of repeating aliphatic units connected by amides. Aliphatic compounds are open-chain materials formed by carbon and hydrogen atoms, such as methane and ethylene.

Spontaneous electric polarization

Nylon is characterized by the number of carbon atoms in the repeating aliphatic units. When this number is odd, nylon can be ferroelectric with spontaneous electric polarization. This type of nylon can therefore be used to make capacitors. Together with their mechanical properties, ferroelectricity makes odd nylons ideal candidates for a range of applications.

According to the team it is a challenge to “construct smooth, optically transparent, pinhole-free solution processed odd-nylon films that are crystallized in the ferroelectric phase”.

The team turned to solution processing, which is a low-cost technique that can be performed at room temperature. Nylons are insoluble in most common solvents, so the first step in the solution processing of nylons is to find the right solvent. Anwar and colleagues found that a mixture of trifluoroacetic acid (TFA) and acetone has the right properties to be used in solution processing of low number odd nylon thin films.

Desired crystalline phase

Nylons can solidify in different crystalline phases, and ferroelectricity occurs in only one of these possible phases. This is a phase in which the unorganized hydrogen-bonded chain structure enables the polarization of the compound. Before this study this ferroelectric phase of odd nylon had never been created by solution processing at room temperature.

The thin films of nylon are made by spin-coating the solution on a glass substrate. The samples are then placed in high vacuum for solution quenching, which freezes the components in the unorganized phase and removes the remaining solvent.

The authors compared the performance of a nylon-11 ferroelectric capacitor with a capacitor made of conventional ferroelectric polymers. The test focused on the ability of the capacitor to retain the polarized state when it is subjected to continuous stress cycles. The nylon-11 capacitor outperformed the conventional one during a million stress cycles.

The technique is described in Science Advances.

Greta-mania peaks as UN climate summit enters its crunch week

COP 25, the UN climate change summit, has entered its second week here in Madrid. The so-called “high-level” section is when heads of state and environment ministers from around the world join negotiations and make statements on national activities.

But on Monday morning, the media hoard wrestled its way into a press conference hosted by environmental activist Greta Thunberg and colleagues of her Fridays for Future movement. Rather than use the platform to call for climate action herself, Thunberg and co-host the German activist Luisa Neubauer introduced speakers from indigenous communities in North America, South America and Africa.

In the video above, a member of the Wind River Indian Reservation in Wyoming, US, gives a prayer for his people and the climate. In the audio clip below, Thunberg explains why she believes that indigenous voices should be central to climate talks.

Greta Thunberg on the need to listen to indigenous voices

The press conference followed a march for climate action on Friday evening, which organizers claim attracted around 500,000 people.

Climate protest in Madrid — Fridays for Future at Madrid climate protest on 6 December (Courtesy: James Dacey)

The march – which included speeches from Thunberg and the Spanish actor Javier Bardem – was a culmination of the atmosphere of protest that surrounds this UN climate event. Whether it will lead to the “rapid and deep change” advocated by UN secretary general António Guterres in the COP 25 opening ceremony will become clearer as the week unfolds.

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Browse articles by content type

Quantum squeezing boosts performance of LIGO and Virgo gravitational-wave detectors

Subatomic-sized changes

Entangled pairs

A wave of discovery

A decade of Physics World breakthroughs: 2015 – double quantum-teleportation milestone

Portable RFG gel scanner rapidly creates 3D images of radiation fields

A relative journey

Bragg diffraction monitors wound healing, plastic soil and other physical science innovations

Bragg reflector

The physics-based firm that helped spawn the IVF revolution

A decade of Physics World breakthroughs: 2014 – landing a spacecraft on a comet

Scientists find a simple solution for making ferroelectric nylon thin films

Spontaneous electric polarization

Desired crystalline phase

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Subatomic-sized changes

Entangled pairs

A wave of discovery

Bragg reflector

Spontaneous electric polarization

Desired crystalline phase