Monthly Archives: October 2020

A number of pictures

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Posted on behalf of Nina Meinzer, senior editor at Nature Physics

The October issue of Nature Physics marks the journal’s 15th anniversary, complete with a cover on which four experimental images are arranged in such a way to form the number ‘15’. Here Nina Meinzer tells the story of how the images that make the cover were created.

Earlier this year, the Nature Physics editors started to think about ways to mark the journal’s 15th anniversary. Little did we know then that, by October, we would not be able to come together and raise a glass to the occasion, and so the celebration had to be confined to the pages of the journal. We knew early on that we wanted to give our past and present editors a chance to reminisce about their time at the journal, and that turned into a collection of memories of their favourite papers.

But how do you turn those assorted papers into a visual concept to make a cool cover? Once we started thinking about it, it struck us that it’s not unusual to see experimental methods, especially imaging methods, demonstrated with the help of numbers or letters as simple test objects. So we asked some of our authors if they had any images of a 15 (or a 1 and a 5) on their hard drives that we might use for the cover. We were deeply moved by the response: although nobody had the sort of thing we were looking for on file, they offered to take some data especially for us — in August, in the middle of a pandemic.

Our art editor then took four of these images and arranged them into a collage to create one big number 15. Bringing together methods from different areas of physics reflects the aim of Nature Physics itself to be a platform for the entire physics community.

What are the methods used to create the images that eventually made up the anniversary cover?

Credit: Hugo Defienne, Daniele Faccio and Alex Wing

Quantum holography (Hugo Defienne & Daniele Faccio, University of Glasgow)   

“Holography is a widely used imaging technique that can be applied to the full electromagnetic spectrum, from X-rays to radio waves and relies on the coherence properties of these waves to extract information from interference patterns.

We have recently extended holography to the case of intrinsically incoherent waves, so that no phase information can be retrieved from a classical interference measurement. Instead, the phase information is now encoded and decoded using entanglement. Entangled photon pairs are used to probe complex objects of which amplitude and phase components are retrieved by imaging the spatial structure of entanglement. As an example, the image on the cover shows the quantum holographic image of the number 15 imprinted onto a spatial light modulator. See also the preprint for more details”

Self-assembly (Serim Ilday, Bilkent University – UNAM) 

Credit: Serim Ilday and Alex Wing

Credit: Serim Ilday and Alex Wing

 “These are microscopy images. Each dot forming the number ‘15’ is a laser beam. Laser pulses that get absorbed by the liquid heat it. The rest, untouched by the laser pulses, remains cold. The liquid starts flowing from the hot to the cold regions, just like in a steam engine. The flows carry polystyrene spheres (red image) and E. coli bacterial cells (green image) towards the beam spots. When they exceed a threshold number, particles and cells slow down the flow the same as the water slows down when you drain it over a sieve. Then, their numbers grow further and write ‘15’.

The recipe? Couple an ultrafast laser to a microscope through a series of optical elements, including a spatial light modulator, which divides a single beam into multiple beams. Cinema projectors have at least one of these for precisely the same reason. Sandwich a thin liquid layer containing the material of interest between two glass slides. Put it under the microscope and shine the laser. Record using a camera. Enjoy!”

Quantum gas microscope (Immanuel Bloch, Max Planck Institute of Quantum Optics)

Credit: Immanuel Bloch and Alex Wing

“The ‘birthday candles’ forming the ’15’ are individual atoms fluorescing in ultra-high vacuum. Lithium-6 atoms are cooled down to around a billionth of a degree above absolute zero and trapped using laser beams. By interfering three pairs of beams, an optical lattice is created which forces the atoms onto a micrometre-spaced regular grid.

An additional custom-shaped laser-pattern coaxes them into the shape of the ’15’. Visible light is then scattered off the atoms and collected with a microscope objective and a single-photon sensitive camera. During illumination, the atoms need to be hindered in heating up via continuous laser cooling. The resulting black-and-white photo is finally coloured. When the atoms are not sending special birthday greetings, they simulate the quantum mechanical behaviour of complex many-body systems.”

 

 

Five inspiring women

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Ada Lovelace (1815-1852), was an English mathematician and is regarded as the first person to recognise the potential of computing power and programming. Since 2009, the second Tuesday of October has been commemorated as Ada Lovelace day, an international celebration of the achievements of women in science, technology, engineering and maths (STEM). Here we celebrate the stories of five pioneering physicists.

 Caroline (Lili) Bleeker1,2 (1897-1985) 

University Museum Utrecht / Public domain

Caroline Bleeker was a Dutch physicist and entrepreneur. She earned her PhD in 1928 from the University of Utrecht, in the Netherlands. Her thesis was on spectral measurements of alkali metals. After her PhD, she started a consultancy to advise companies on scientific instruments. This project then evolved into opening her own factory to produce equipment, particularly focussing on optical components.

During the German occupation of the Netherlands in the second world war, Bleeker hid Jewish people in her factory. In 1944, the factory was raided by German troops, but Bleeker, who spoke fluent German, was able to distract the soldiers while those who were hiding escaped through the garden. After this, the factory was closed down by the Germans and Bleeker herself had to go into hiding for the remainder of the war.

After the war, the factory reopened and Bleeker worked with her long-term friend Fritz Zernike to produce the world’s first complete phase contrast microscopes. They filed the patent on this together, and in 1953, Zernike won the Nobel prize for this invention.

Elizaveta Karamihailova3  (1897-1968)

Physmuseum / Public domain

Elizaveta Karamihailova was a nuclear physicist and the first woman to become a professor in Bulgaria. She earned her PhD in 1922 from the University of Vienna in Austria. After this, she worked at the Institute of Radium Studies in Vienna with Marietta Blau. Together, they observed a previously unknown radiation from polonium in 1931. Later, this was confirmed by James Chadwick as neutron radiation, which led to him winning the Nobel prize in 1935.

After further postdoctoral work at the Cavendish Laboratory in Cambridge, UK, Karamihailova returned to Bulgaria in 1939, where she set up the first atomic physics course at the University of Sofia. She no longer had the equipment to continue her previous work on ionisation, and so she turned to studying cosmic rays using photographic plates. In 1944, a left-wing uprising took place in Bulgaria and the authorities labelled Karamihailova “unreliable” due to her anti-communist views. She could no longer travel abroad and spent the rest of her career in Bulgaria.

湯浅年子, Toshiko Yuasa4 (1909 –1980) 

朝日新聞社 / Public domain

Toshiko Yuasa earned a degree from Tokyo Bunrika University in 1934 to become the first female physics graduate in Japan. She started teaching there and began her research career in molecular spectroscopy. In 1940, Yuasa moved to France to continue her research, despite the beginning of the second world war. She worked with Frederic Joliot-Curie (son-in-law of Marie Curie) on radioactivity, earning her PhD in 1943.

After the Allied liberation of France in 1944, Yuasa had to leave for Berlin, where she built a double-focussing beta spectrometer. In 1945, Soviet troops ordered Yuasa to return to Japan. She made her way back through Siberia, carrying the spectrometer on her back, arriving in Japan just before it surrendered. However, the US occupying forces in Japan would not allow her to continue her research in nuclear physics, so she could only teach. In 1949, she returned to France as a researcher for the Centre national de la recherche scientifique (CNRS), where she remained for the rest of her career.

سميرة موسى‎, Sameera Moussa5,6,7 (1917–1952) 

Al Ahram Daily news Paper / Public domain

Sameera Moussa was an Egyptian nuclear physicist who worked on atomic energy and was the first women to be a lecturer at the University of Cairo. In the 1940s, Moussa discovered a way to split up atoms of cheap metals, such as copper, which would make the medical applications of nuclear technology much more affordable. However, against the backdrop of the second world war and the detonation of the first nuclear bombs, Moussa was keen to advocate for the regulation of nuclear technology. In 1952, she organised a conference on “Atomic Energy for Peace” which inspired the US program “Atoms for Peace”.

Moussa received a Fulbright scholarship and travelled to the University of California for further research. She was the first non-US citizen to be given access to the top-secret US atomic facilities, which caused some controversy. In 1952, she died when her car was driven off a cliff. Moussa is believed to have been assassinated as the driver was not found, and it is thought that he jumped out of the car. Raqia Ibrahim, an Egyptian-Israeli actress, was accused of murdering Moussa on behalf of the Israeli Mossad who were concerned at the idea of Egypt acquiring a cheap atomic bomb.

পূর্ণিমা সিনহা, Purnima Sinha8,9 (1927–2015) 

https://www.livehistoryindia.com/herstory/2019/05/26/dr-purnima-sinha-pioneering-physicist / CC BY-SA

Purnima Sinha studied physics at the University of Calcutta in the late 1940s. During her time as an undergraduate, she was taught by Satyendra Nath Bose, who encouraged her to join his research group and undertake a PhD in X-ray spectroscopy. Sinha became the first Bengali women to receive a doctorate in physics in 1956. The PhD students worked together to collect scrap army surplus equipment which was readily available after the second world war to build equipment for their research. Sinha studied the structure of clay; later, she joined a biophysics department at Stanford University and found structural similarities between the geometries of clay and of DNA.

In addition, to her scientific pursuits, Sinha was an accomplished musician, painter and translated many science books into Bengali. In 1970, she published an anthropology book on Indian folk music. Sinha was actively involved in Bengali Science Association, which had been set up by Bose. After retirement, she also created an informal school for children of ethnic minorities.

 

References

  1. Dr. Caroline Emilie Bleeker, physicist and businesswoman. Accessed 12.10.2020
  2. Lili Bleeker, Wikipedia Accessed 12.10.2020
  3. Elizaveta Karamihailova, Wikipedia Accessed 12.10.2020
  4. Toshiko Yuasa, Wikipedia Accessed 12.10.2020
  5. Sameera Moussa, Wikipedia Accessed 12.10.2020
  6. Abdulaal, M. The Story of Sameera: World-Renowned Egyptian Nuclear Scientist, Egyptian Streets (2018) Accessed 12.10.2020
  7. Al-Youm, A. Raqia Ibrahim: Egyptian Jewish actress recruited by Israel to prevent Egypt owning nuclear bomb. Egypt Independent (2014) Accessed 12.10.2020
  8. Purnima Sinha, Wikipedia  Accessed 12.10.2020
  9. Katti, M. Dr Purnima Sinha: Pioneering Physicist. Live History India (2014) Accessed 12.10.2020

Achieving a Bose–Einstein Condensate from my living room during lockdown

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During the COVID-19 lockdown which led to the closure of many labs around the world, Dr. Amruta Gadge, a postdoctoral researcher in the Quantum Systems and Devices group at the University of Sussex*, made headlines for remotely setting up a Bose–Einstein condensate from her living room. Here, she tells us her story.

When the UK government announced the national lockdown on 23rd March due to the pandemic, my lab at the University of Sussex was forced to temporarily close its doors.  We of course had a strong inkling this was coming, and rushed to get ourselves in order before it happened. In my laboratory, we were determined to keep our experiments going as best we could although we had never run them remotely before. Without being able to set foot in the labs, bar a few essential maintenance visits, the only way to continue working on our experiments was to use dedicated remote control and monitoring technology.

Dr Amruta Gadge adjusting a laser pre lockdown{credit}Rebecca Bond{/credit}

Pre-lockdown, I was part of a team building an apparatus to produce Bose-Einstein condensates (BECs).  A BEC consists of a cloud of hundreds of thousands of rubidium atoms, which have been cooled down to nanokelvin temperatures using lasers and magnetic fields.  At such temperatures the cloud suddenly takes on different characteristics, with all atoms behaving together as a single quantum object. This object has such low energy that it can be used to sense very low magnetic fields, a property we are making use of to probe   novel materials such as silver nanowires , silicon nitride nano membranes or to probe ion channels in biological cells.

We had started assembling this system just a few months before, and were looking forward to reaching a big milestone in the lab – producing our first BEC.  Time was short!  To run such an experiment from home was no easy feat, with large and complex laser and optics set-ups in state-of-the-art labs – which couldn’t just be transported.  In the days leading up to lockdown, equipment, chairs, and computers were being ferried to various homes, deliveries of equipment were diverted and protocols for remote access and online control were put in place.

Ultra-cold atom experiments are very complex. Obtaining a BEC involves a large amount of debugging and optimising of the experimental sequence. When not in the lab, at times it felt almost impossible to debug. We set up software control for the equipment, such as oscilloscopes, vacuum pumps, and others. However, the tool that played the most important role was our environmental monitoring system. Trapped cold atoms are extremely sensitive to any variations in the environmental conditions. Changes in the ambient temperature of the lab, humidity, residual magnetic fields, vacuum pressure, and so on, result in laser instability, polarisation fluctuations or changes in the trapping fields. All of these effects lead to fluctuations of the number of trapped atoms, as well as their position and temperature.

Debugging the system is a long process, but this can be greatly helped by monitoring the environmental conditions at all times. This may sound elaborate, however with the rising popularity of time series databases and data visualisation software, it is possible to develop a convenient monitoring system. We made use of cheap and easily programmable microcontrollers for data collection, and two popular open source platforms, InfluxDB and Grafana, for storing and visualising the data, respectively. We set up a large network of sensors throughout the labs, aimed at monitoring all the parameters relevant to the operation of the experiments. If atom numbers fluctuated, or something wasn’t performing well, we could quickly narrow down the problem by looking at our Grafana dashboards. This meant that our experimental control sequence could be quickly tweaked from home for compensating the environmental fluctuations, and the monitoring system proved to be an extremely useful tool in achieving BECs remotely.

Dr Amruta Gadge working from home with an image of her BEC on screen{credit}Amruta Gadge{/credit}

We were installing a new 2D magneto-optical trap atom source in the lab, and managed to see a signal from it just the day before the lockdown. I remember clearly that I was very worried that lockdown was going to delay the progress of our experiment significantly.  .  However, thankfully we could keep operating remotely, and managed to achieve our long-awaited first BEC from my home.

I was very excited when I saw the image of our first BEC. I had spent the whole day optimising the evaporation cooling stage. It was past 10pm, and I was about to stop for the day and suddenly the numbers started looking promising. I continued tweaking the parameters and in just few attempts, I saw the bimodal distribution of the atoms — a signature of a BEC. It was strange to have no one there to celebrate with in person, but we instead got together to hold celebrations virtually — something we are all getting used to now. I was really hoping to get the first BEC of our experiment before moving to my next post-doc, and having it obtained remotely turned out to be even more gratifying.

 

*Dr. Amruta Gadge is now a post-doctoral researcher in the cold atoms and laser physics group at the Weizmann Institute of Science, Israel.