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Home » Page 1073

Gravity measured using a Bose–Einstein condensate on a chip

A new sensor that measures the local acceleration due to gravity using a Bose–Einstein condensate (BEC) of ultracold atoms has been made by physicists in Germany, the US and Canada. While the prototype device is not as accurate as commercial gravimeters, its makers say it could be made much smaller and much more accurate than existing devices.

Atoms can be used to measure the acceleration due to gravity by cooling a gas of them to near absolute zero and then dropping them along two different paths in an interferometer. The quantum interference that occurs when the paths converge at a detector provides a very good measure of gravity, with commercial atom interferometers able to measure the acceleration to within one part in 108. Such measurements are invaluable for geological exploration because the presence of certain minerals can be spotted by seeking tiny variations in gravity at the Earth’s surface.

While these ultracold atom gravimeters are on a par with conventional absolute gravimeters based on macroscopic falling masses, their accuracy could be improved a lot by using a BEC. In a conventional atomic gravimeter, the ultracold atoms form a diffuse gas roughly a millimetre in size and a major cause of uncertainty is that the laser pulses used to control the atoms are not spatially uniform on that length scale. A BEC – formed by cooling a gas of atoms with integer spin until they condense into a single quantum state – reduces this uncertainty because it squeezes the atoms into a region that is about 100 times smaller.

Tiny vacuum chamber

Created by Ernst Rasel of Leibniz University of Hannover and colleagues, the BEC gravimeter has at its heart a chip a few centimetres in size that contains a tiny vacuum chamber. Lasers and magnetic fields trap about 15,000 rubidium atoms at the top of the chip, where they are cooled to temperatures of a few nanokelvin to create a BEC.

The BEC is then allowed to fall about 1 cm through the chamber and, as it does so, a series of laser pulses is fired at the BEC, deflecting the atoms into different paths to create an interferometer. It takes about 10 ms for the atoms to complete their free fall, but the sensitivity can be improved if this time is extended using a laser pulse to bounce the atoms back up when they reach the bottom of the chip. The atoms are then allowed to fall back down again, increasing the free-fall time by a factor of five.

Rasel and colleagues were able to measure the acceleration of the atoms with an accuracy of about one part in 107 – at least an order of magnitude worse than commercial gravimeters. Writing in Physical Review Letters, the researchers point out that their gravimeter was operated in a “rough environment without access to any vibrational shielding”, which caused much of the measurement uncertainty. By reducing the vibrations and doing other improvements, Rasel and colleagues reckon the gravimeter could operate with an uncertainty of less than one part in 109 and fit inside of a backpack.

What is spintronics?

The word “spintronics” is a portmanteau of spin and electronics. That’s because this emerging field of applied physics offers an alternative to conventional electronics – using an electron’s spin instead of its charge to carry information. In this short video, Christoph Boehme – a condensed matter researcher of the University of Utah in the US – introduces spintronics to the uninitiated. Boehme takes it back to basics by explaining what physicists mean by an electron’s spin and how this can be exploited to encode information within circuitry. He also introduces some of the possible applications and beneficiaries of spintronics such as websites dealing with big data sets.

This video is part of our 100 Second Science series, in which researchers give concise presentations covering the spectrum of physics.

Flash Physics: Graphene-based loudspeaker, new schedule for ITER, India joins CERN

“Consumer-ready” loudspeaker is made from graphene oxide

The first “consumer-ready” loudspeaker made from graphene oxide has been unveiled by the Canada-based company ORA. Researchers at the start-up company made their loudspeaker from a grapheme-oxide-based composite material dubbed GrapheneQ. The material has properties similar to pristine graphene, which is a sheet of carbon just one atom thick. GrapheneQ is made by reducing graphene and then adding a proprietary blend of cross linkers to make the composite. The material is designed to have a low “Q resonance”, which means that it requires less damping (especially at low frequencies) than commercial devices to prevent unwanted frequency responses. This means that the device can operate at just a few nanoamps and so uses much less power than conventional speakers – a real advantage if it were to be employed in portable devices. Less damping at lower frequencies also means that the bass and treble response are both extended, which drastically improves the fidelity of the music being reproduced. “GrapheneQ is also very inexpensive to produce (membranes cost as little as $0.02 in raw materials), is easily shaped into 3D forms, and is scalable,” explains ORA co-founder Xavier Cauchy. A longer version of this article first appeared on nanotechweb.org.

ITER council endorses new “baseline” schedule

The ITER Council has approved an updated schedule for the huge fusion experimental facility that is currently being built in Cadarache, France. At a meeting held from 16 to 17 November, the council approved the plan that was proposed by the ITER organization earlier this year with first plasma set for 2025 – a delay of five years – and ITER only moving onto deuterium-tritium fuel in 2035. ITER is a collaboration between China, the EU, India, Japan, Russia, South Korea and the US that aims to demonstrate that nuclear fusion can generate useful energy. It will involve a giant doughnut-shaped chamber, known as a tokamak, which will use strong magnetic fields to contain a heated plasma of deuterium and tritium at a temperature of tens of millions of degrees so that atomic nuclei collide and fuse. In theory, the reactor will produce 10 times the power it takes to heat it. The slip in the schedule was initially announced in June after French nuclear physicist Bernard Bigot, former head of France’s Alternative Energies and Atomic Energy Commission, was brought in as ITER director general in 2015 to shake up the organization and draft a credible schedule. In its November meeting, ITER Council reported that all 19 project milestones for this year had been completed on time and on budget.

India will become associate member state of CERN

Photograph of dignitaries signing the CERN-India agreement
CERN director general Fabiola Gianotti (left) and Sekhar Basu, who is secretary of the Department of Atomic Energy (DAE) of the Indian government, sign the agreement. (Courtesy: CERN)

An agreement that will see India join CERN as an associate member state has been signed by CERN director general Fabiola Gianotti and Sekhar Basu, who is secretary of the Department of Atomic Energy (DAE) of the Indian government. Associate membership will allow India to take part in meetings of the CERN Council and Indian physicists will be eligible for staff appointments at the lab. Indian companies will also be able to bid on CERN contracts. Indian physicists have been involved with the Geneva-based particle-physics lab for more than 50 years, and in 1996 the Indian Atomic Energy Commission contributed to the construction of the Large Hadron Collider (LHC) as well as the CMS and ALICE experiments. The country also hosts Tier 2 centres of the LHC Computing Grid in Mumbai and Kolkata. India was granted observer status at CERN in 2002 and the DAE has since been involved with a number of facilities and experiments at CERN including the ISOLDE radioactive ion-beam facility. “Becoming associate member of CERN will enhance participation of young scientists and engineers in various CERN projects and bring back knowledge for deployment in the domestic programmes,” says Basu. India’s membership will begin once the agreement gains final approval from the Indian government.

 

  • You can find all our daily Flash Physics posts in the website’s news section, as well as on Twitter and Facebook using #FlashPhysics. Tune in to physicsworld.com later today to read today’s extensive news story on an atomic gravimeter on a chip.

China forges ahead in global research

China is performing “outstanding” research in a number of emerging scientific topics, putting the country’s output on a par with the UK but still behind the US. That is the conclusion of a new study by the Chinese Academy of Sciences (CAS) and the scientific data company Clarivate Analytics. The Research Fronts 2016 annual report identifies 100 “hot” and 80 “emerging” research areas based on citation analysis of papers published in 2015.

The research areas – divided in various fields of science – reflect global interest in specific topics that have resulted in “core” journal articles. These articles are defined by an algorithm that takes into account, among other things, the time of publication and how frequently an article is cited by other papers in the same area. In physics, for instance, the hottest research pursuits last year included the detection of dark matter and experiments that measure neutrino oscillations. Research into properties and applications of black phosphorus – a 2D material also called phosphorene because of its similarity to graphene – was also identified. The study of topological materials called Weyl semimetals was also named as a hot topic in physics.

China has a significant gap with the US, and fierce competition with the UK
Research Fronts 2016

Six countries – China, France, Germany, Japan, UK and US – made the greatest contributions in the 180 research areas, according to the report. The US retained its leadership, with its researchers publishing core papers in 152 of the 180 areas, ranging from the hunt for dark matter to the health impact of electronic cigarettes. The UK, meanwhile, contributed core papers in 90 research topics, covering more areas than China’s 68. However, China had top-cited papers among the core papers in 30 research areas, which is more than twice that of the UK. “China has a significant gap with the US, and fierce competition with the UK,” the report says, adding it was likely that China would soon overtake the UK.

Spending growth

One factor in China’s success is that it invested more than $400bn on R&D last year, second only to the US. In 2015, more than 2% of China’s gross domestic product (GDP), adjusted by purchasing power, was spent on research. The rapid increase of government investment has spurred the construction of many large facilities, including the world’s largest single-aperture telescope, the longest quantum-communication network and the first quantum satellite. CAS president Chunli Bai says that the Chinese government is expected to support many of the identified areas over the next five to 10 years. “These breakthroughs may change the future pattern of the world,” says Bai.

Flash Physics: Shrinking gels, masculine culture discourages female physicists, Carlos Frenk bags Born medal

Study explains why some materials shrink under stress

When a conventional soft material is placed between two surfaces that then move across each other in opposite directions, the material tends to bulge out at right angles to the motion of the surfaces. However, there are some gel-like materials such as blood clots that do the opposite when under stress – and understanding why has puzzled physicists for some time. Now, Daniel Bonn at the University of Amsterdam and colleagues have performed calculations and experiments that they say can explain the phenomenon. Materials that shrink under stress tend to comprise networks of filaments that also contain water. When the team modelled such materials they found that when the gaps between the filaments were small, the water could not easily move within the gel – and the materials bulged when stressed. When the pores are larger, however, the water can flow more easily when stressed. This allows the network to shrink in the directions perpendicular to the stress as the water flows away from the stressed regions. The team was also able to observe this behaviour in the lab and the results – which are reported in Physical Review Letters – could prove useful to scientists developing artificial tissues.

Women discouraged by masculine culture in physics

Photograph of a woman working with equations
Counter culture: women are discouraged by masculine culture (Courtesy: iStock/ALLVISIONN)

An analysis of more than 1000 papers on gender disparity in science, technology, engineering and mathematics subjects has revealed three main reasons why women are underrepresented in those subjects at undergraduate level in the US. The research, led by Sapna Cheryan, a psychologist at the University of Washington in Seattle, found that the key factors are a lack of sufficient early experience in these subjects, the existence of masculine cultures and gender gaps in self-belief. The research focused on the six science and engineering fields with the highest numbers of undergraduate degrees: biology, chemistry, mathematics, physics, engineering and computer science. In the US, biology, chemistry and mathematics are studied by almost equal numbers of men and women, while physics, engineering and computer science are male dominated, with less than 20% of undergraduate degrees being awarded to women. The analysis revealed three overarching reasons why women participate less in physics, engineering and computer science, the most significant of which was the existence of masculine cultures. Cheryan says that there are three main characteristics of the masculine cultures they identified: male-oriented stereotypes about the people in these fields, negative stereotypes about women’s abilities and few female role models. “These signal to girls and women that they do not belong to the same extent as their male peers,” Cheryan told Physics World. The research is described in Psychological Bulletin.

Cosmologist Carlos Frenk wins 2017 Max Born Medal

Dark-matter medallist: Carlos Frenk has won the 2017 Max Born Medal
Dark-matter medallist: Carlos Frenk has won the 2017 Max Born Medal (Courtesy: The Peter and Patricia Gruber Foundation)

The 2017 Max Born Medal for outstanding contributions to physics has been won by the cosmologist Carlos Frenk. Originally from Mexico, Frenk is director of the Institute of Computational Cosmology at the University of Durham in the UK. He bagged the medal for his pioneering work on the theory of cold dark matter (CDM), which explains the formation of galaxies and other large structures in the universe. The medal is given jointly by the Institute of Physics and the German Physical Society and includes a prize of €3000. In odd-numbered years the award is given to a physicist based in the UK or Ireland and presented in Germany. In even-numbered years the winner is based in Germany and travels to the UK or Ireland to accept the prize. In 2015 Frenk was a consultant on The World Machine, which was a science-themed sound-and-light show projected onto the façade of Durham Cathedral. He speaks about that experience in “The cathedral and the cosmos“.

 

  • You can find all our daily Flash Physics posts in the website’s news section, as well as on Twitter and Facebook using #FlashPhysics. Tune in to physicsworld.com later today to read today’s extensive news story on how physics research is improving in China.

Inspiring young physicists, telescope buyer’s guide, time-travelling pyramid builders

Sunlight calculator: Asimina Arvanitaki (Courtesy: PI)
Sunlight calculator: Asimina Arvanitaki. (Courtesy: PI)

By Hamish Johnston

Have you ever wondered what inspires talented physicists to pursue careers in physics? To try to answer that question, the Perimeter Institute for Theoretical Physics (PI) in Canada has produced a set of tiles that explain how some famous physicists – and some up-and-coming stars – became hooked on physics at a young age. An early love of back-of-the-envelope calculations seems to have set the stage for the PI’s Asimina Arvanitaki as she explains in the above tile. Can you guess which Nobel laureate used to stare at a clock pendulum for hours to try to figure out how it worked? The answer to that teaser and much more can be found in “How great scientists get hooked on science”.

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Do physicists avoid reading papers with lots of equations?

Including large numbers of mathematical equations in a research paper could impede the effective communication of the physics it describes. That is the controversial conclusion of a study of citation numbers by researchers from the University of Exeter in the UK, who advocate for the more accessible reporting of theoretical research. However, some physicists disagree with their analysis and conclusion.

Mathematics plays a fundamental role across the breadth of the sciences, underpinning the development of theoretical concepts. However, evolutionary biologists Tim Fawcett and Andrew Higginson noticed that many experimental biology papers seemed to lack a solid theoretical basis. They also found that theoretical biology papers were often neglected by the research community and that many evolutionary biologists confessed to being deterred by equation-dense papers.

These observations inspired the duo to look into how maths is presented in 649 papers from three major ecology and evolution journals. Using generalized linear models to analyse how often papers are cited, they found a negative correlation between a paper’s equation density and the number of citations it received. Indeed, there were 28% fewer citations on average for each additional equation per page.

Valuable papers may be ignored if they are not made accessible
Andrew Higginson, University of Exeter

No effect in physics

This result raised an important question: could this trend be fixed with improved mathematics training for biologists, or does it also exist in fields with a traditionally greater reliance on math, like physics? This was investigated in 2015 by the physicist Jonathan Kollmer of the Friedrich-Alexander University Erlangen, Germany, and colleagues. They found no evidence for the correlation in the citations of 1000 papers that appeared in Physical Review Letters (see “Are physicists afraid of mathematics?“). In that same study, Kollmer and colleagues also questioned the original analysis of biology citations by Fawcett and Higginson.

Now, Fawcett and Higginson have done their own analysis of Physical Review Letters papers and come to a different conclusion. They found an average 6–8% decrease in citation frequency for each additional equation per page. The duo suggest that this indicates that there are real and widespread barriers to the communication of mathematical work – independent from the levels of mathematical training, or any stigma about doing well in mathematics.

“Ideally, the impact of scientific work should be determined by its scientific value, rather than by the presentational style. Unfortunately, it seems valuable papers may be ignored if they are not made accessible,” says Higginson. “This presents a potentially enormous barrier to all kinds of scientific progress.”

Fawcett adds: “It takes time to scrutinise the details of a technical article – even for the most distinguished physics professors – so with many competing demands on their time, scientists may be choosing to skip over articles that take too much effort to digest.”

More explanatory text

But what might be done to address this communication issue? The researchers recommend both the use of more explanatory text to support equation-heavy theoretical papers, along with the relocation of non-essential equations – such as those describing the intermediate steps to solutions – to appendices where they will not affect the equation density of the main text.

This question can hardly be addressed by conducting purely correlative studies as they give no insight about any causal relationship
Jonathan Kollmer, Friedrich-Alexander University Erlangen

“Physicists need to think more carefully about how they present the mathematical details of their work, to explain the theory in a way that their colleagues can quickly understand,” says Fawcett.

“Anecdotally, I could well believe that the finding of a negative correlation between mathematical density and citations rates is real,” comments John Rayner – a physicist and science communication researcher at the Australian National University, who was not involved in this study. He adds: “If utility and clarity are the hallmarks of a high citation rate, then the circumspect use of mathematics can only help.”

Kollmer, however, remains unconvinced. “This question can hardly be addressed by conducting purely correlative studies as they give no insight about any causal relationship,” he says. Several reasons could account for such a correlation, he adds – such as the population differences between more theoretical and experimental research areas – and the correct explanation “cannot be evidenced by pure statistical analysis but would need sociological and more elaborated research”.

Fawcett and Higginson are now using the citation results to explore how the influence of theory spreads through scientific literature across different disciplines, along with investigating the root of mathematical anxiety, and the impact of promotion and funding criteria on the behaviour of scientists.

Fawcett and Higginson’s study is described in the New Journal of Physics and Kollmer and colleagues have since published a reply in the same journal.

Flash Physics: Optical clock in space, Richard Garwin wins presidential medal, lighting the cosmic web

First optical clock in space could improve GPS

The first optical clock to be operated in space has been launched by Matthias Lezius and colleagues at the Germany-based Menlo Systems. Based on a frequency-comb laser system, the optical clock operates at a frequency that is about 100,000 times higher than that of the microwave-based atomic clocks that are currently used on global-positioning-system (GPS) satellites. The optical clock is about 22 cm in size and weighs 22 kg. Its power consumption is about 70 W, which makes it suitable for satellite applications. Although this prototype optical clock can only operate at about one tenth the accuracy of today’s GPS atomic clocks, Lezius’ team is now working on a new version of the clock that promises to improve this accuracy by several orders of magnitude – which could boost the accuracy of GPS. The current clock was tested on board a research rocket that flew a 6 min parabolic flight. The next version of the optical clock is scheduled for testing in 2017. The research is described in Optica.

Physicist Richard Garwin wins US Presidential Medal of Freedom

The physicist and advocate of strategic nuclear-arms reduction Richard Garwin will receive a Presidential Medal of Freedom from US president Barack Obama. Garwin, who is 88, was a PhD student of Enrico Fermi at the University of Chicago before designing the first hydrogen bomb in 1952 under Edward Teller at Los Alamos National Laboratory. He then moved to IBM’s Thomas J Watson Research Center, where he is an IBM fellow emeritus. At IBM he worked on a broad range of topics including condensed matter, particle physics and gravitation. He also applied his skills to the development of touch screens, laser printers and intelligence-gathering technologies. Garwin served as a scientific adviser to presidents Kennedy, Johnson and Nixon, which is when he developed his long-standing interest in nuclear non-proliferation (see video). The medal is the highest civilian honour in the US and it will be given to Garwin and 20 other winners at a ceremony at the White House on 22 November.

Fast radio burst lights up cosmic web

The radio pulse FRB 150807
Short and sharp: The radio pulse FRB 150807. The colour shows the frequency of the waves, which is like the colour of light. The brightness varies with frequency due to a process termed ‘scintillation’, which is caused by the twinkling of the burst in the cosmic web. This scintillation is the fingerprint of turbulence in the cosmic web and tells us that the web is very placid. (Courtesy: Dr Vikram Ravi/Caltech and Dr Ryan Shannon/ICRAR-Curtin/CSIRO)

A brilliant burst of radiation known as a fast radio burst (FRB) that has travelled over a billion light years has unexpectedly revealed information about the cosmic web – the large-scale structure of the universe. A team led by Ryan Shannon at the International Centre for Radio Astronomy Research (ICRAR) and Vikram Ravi of the California Institute of Technology says that the latest FRB – one of 18 to be detected to date – is one of the brightest seen. The flash was captured by CSIRO’s Parkes radio telescope in New South Wales, Australia. FRBs are extremely rare, short but intense pulses of radio waves, each only lasting about a millisecond. “This particular FRB is the first detected to date to contain detailed information about the cosmic web – regarded as the fabric of the universe – but it is also unique because its travel path can be reconstructed to a precise line of sight and back to an area of space about a billion light-years away that contains only a small number of possible home galaxies,” says Shannon. The cosmic web is very difficult to spot because most of the plasma and gas it contains is very faint. It is usually detected when large sections of it are lit up briefly, for example by a bright quasar or a FRB. This particular flash reached the Parkes radio telescope mid last year and is described in Science.

 

  • You can find all our daily Flash Physics posts in the website’s news section, as well as on Twitter and Facebook using #FlashPhysics. Tune in to physicsworld.com later today to read today’s extensive news story on why some physicists do not like mathematics.

Texas gravitational-wave research centre returns misused funds

The University of Texas Rio Grande Valley (UTRGV) in the US has had to repay almost $5m in research grants that were allegedly misused by the Center for Gravitational Wave Astronomy (CGWA). The UTRGV, which opened in August 2015, is repaying the grants that were given to the CGWA when it was part of the University of Texas at Brownsville (UTB).

The state of Texas created the UTRGV by consolidating the UTB with the University of Texas–Pan American in Edinburg, and the UT Regional Health Center in Harlingen, which were dissolved after the new university started operation. At its founding, the UTRGV assumed all the assets and liabilities of the universities it replaced.

Crucial role in LIGO

Founded in 2003, the CGWA played a significant role in developing the basic technologies, instrumentation and algorithms involved in the first detection of gravitational waves in September last year by the Laser Interferometer Gravitational-wave Observatory (LIGO) in Washington and Louisiana.

But according to The Monitor – a local Texas newspaper – an internal audit carried out by the University of Texas as part of the closure of UTB discovered that the centre had misused nearly $2m in research grants from NASA, the National Science Foundation, and the Department of Defence over a period of six years.

Another audit revealed apparent misuse of almost $3m in grants from the Texas government from 2012 to 2015. The auditors indicate that the grants had been used to pay faculty members who were teaching rather than carrying out research.

Unexpected hole

The $5m repayment leaves an unexpected hole in the UTRGV’s $478m annual budget. “In connection with audits conducted last year at both legacy institutions, issues with expenditures related to grants and to benefits proportionality were identified at the University of Texas at Brownsville,” the UTRGV noted in a statement to Physics World. “Those findings resulted in UTRGV returning almost $5m to the appropriate state and federal agencies. UTRGV is currently evaluating the impact, if any, these repayments will have on future operational decisions.”

Just how the misuse of the grants occurred, however, remains unexplained. “While my department, along with the university, continues to evaluate the situation, I have been asked not to comment until the facts have been established,” physicist Mario Díaz, who is director of the CGWA, told Physics World.

American angst

Danger ahead – Donald Trump’s election as US president will not be business as usual for science policy. (Courtesy: iStock/uschools)

By Matin Durrani

Like many people, I’m fearful of the imminent Donald Trump presidency, given the many sexist, racist and otherwise unpleasant remarks he made during the US election campaign. However, his slogan – “Make America great again” – proved powerfully effective for many voters. Who, after all, could disagree with renewed domestic glory? Sadly, Trump’s plans for achieving that goal – what little we know of them – are based on such ill-informed and ignorant views that he could damage America’s long-standing leadership in many areas, including science.

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