Quantum 'paparazzi' film photons in the act of pairing up

2015-04-22

(Press-News.org) In the quantum world of light, being distinguishable means staying lonely. Only those photons that are indistinguishable can wind up in a pair, through what is called Hong-Ou-Mandel interference. This subtle quantum effect has been successfully imaged for the first time by two doctoral students from the Faculty of Physics at the University of Warsaw.

Physicists have long known that photons can become bunched together. However, technological limitations have prevented the phenomenon from actually being observed directly. Only recently has this feat been achieved by two doctoral students from the Faculty of Physics at the University of Warsaw (UW). In an article just published in the renowned optical journal Optics Letters, Micha? Jachura and Rados?aw Chrapkiewicz presented a film sequence clearly showing photons forming pairs.

"We are the first to have filmed individual photons in a very interesting situation, 'pairing off' as a consequence of an effect known as Hong-Ou-Mandel two-photon interference," says doctoral student Micha? Jachura. He playfully expands upon this 'matrimonial' metaphor: "When carrying out our experiment we felt a bit like paparazzi. We were wielding an advanced camera of the latest generation, the exclusive 'venue' was the world of quantum mechanics, and the 'celebrities' we wanted to capture in the act were individual photons."

Interference is a phenomenon that can be observed when any wave - be it a light wave, a sound wave, or otherwise - passes through a barrier with more than one aperture (an experiment first carried out by the British physicist Thomas Young). Each aperture then acts as the source of a new wave, and a characteristic pattern of interference fringes forms on the other side of the screen placed behind the barrier. In the case of light waves, we see bright fringes where the wavefronts reinforce one another, and dark fringes where they cancel each other out.

Objects in the quantum world are characterized by a certain surprising property: they may behave either like particles or like waves, depending on how we observe them. If an individual photon behaves like a wave, it can pass through two apertures at the same time and interference fringes will form on the other side of the barrier (in other words, the single photon will interfere with itself). But such interference is only observed if the measurement system does not allow us to ascertain which aperture the photon passed through. If we make it possible to do so (for instance by placing a polarizing plate behind one of the apertures), the photon will immediately behave like a particle and the interference fringes disappear.

In 1987, a group of physicists from the University of Rochester (UR) predicted and observed a subtle quantum effect in an experimental setup involving a beam-splitting plate, which transmits some of the light that falls on it and reflects the remainder. The parameters of the plate can be chosen so that the probability of a given photon being reflected is equal to the probability of its passing through. If one photon is sent towards the plate from one side and another photon from the other side, there are four possible outcomes: both photons may be reflected, both transmitted, one of the photons may be reflected while the other is transmitted, or vice versa. The quantum-mechanical calculations performed by the UR physicists indicated that these various scenarios do indeed occur, but only when the photons impinging the plate are distinguishable, which means they are behaving like particles. But if the photons remain indistinguishable, interference will occur between them. As a result, the two photons become bunched into a pair and always appear together, on one side of the plate or the other.

"The Hong-Ou-Mandel effect had been observed before, but only by using photodiodes, which simply signaled the detection of a photon by sending out an electrical impulse. We were much better equipped, having at our disposal a highly advanced camera built by our research group. This camera, a bit similar to night-vision goggles, consists of an ultra-modern image intensifier and a very sensitive and a low-noise, fast sCMOS sensor. It proved to be so good that we were able to study the behavior of individual particles of light and managed to film their quantum interference," says doctoral student Rados?aw Chrapkiewicz, stressing that the camera design team also included Wojciech Wasilewski, PhD, and Jaros?aw Iwaszkiewicz, Eng. (both from the UW Faculty of Physics).

Using the camera and image intensifier, the UW Physics researchers managed to film the behavior of photons in two situations: when the photons being sent towards the beam-splitting plate were distinguishable and indistinguishable. In the former case the sequence of images shows individual green spots, which represent individual photons being registered, appearing randomly on opposite sides of the plate or together on one side or the other. But the moment the physicists purposefully eliminated the distinguishability, the photons immediately joined together in pairs and left the beam-splitting plate always on the same side, never separately.

"Managing to film two-photon interference is a very important result for quantum optics, as it means that from now on physicists will be able to directly observe spatial optical phenomena that involve single photons," stresses Prof. Tomasz Matulewicz, director of the Institute of Experimental Physics at the UW Faculty of Physics.

This research achievement, made possible by a PRELUDIUM grant from Poland's National Science Centre, represents an important step towards developing efficient methods of detecting quantum states of light and building super-resolution optical microscopes of a new type, capable of registering images using a small number of photons, therefore fully safe to use even with very delicate samples.

INFORMATION:

Physics and Astronomy first appeared at the University of Warsaw in 1816, under the then Faculty of Philosophy. In 1825 the Astronomical Observatory was established. Currently, the Faculty of Physics' Institutes include Experimental Physics, Theoretical Physics, Geophysics, Department of Mathematical Methods and an Astronomical Observatory. Research covers almost all areas of modern physics, on scales from the quantum to the cosmological. The Faculty's research and teaching staff includes ca. 200 university teachers, of which 88 are employees with the title of professor. The Faculty of Physics, University of Warsaw, is attended by ca. 1000 students and more than 170 doctoral students.

CONTACTS:

M.Sc. Rados?aw Chrapkiewicz
Institute of Experimental Physics, Faculty of Physics, University of Warsaw
tel. +48 22 55 32 629
email: radoslaw.chrapkiewicz@fuw.edu.pl

M.Sc. Micha? Jachura
Institute of Theoretical Physics, Faculty of Physics, University of Warsaw
tel. +48 22 55 32 629
email: michal.jachura@fuw.edu.pl

SCIENTIFIC PAPERS:

"Shot-by-shot imaging of Hong-Ou-Mandel interference with an intensified camera"; M. Jachura, R. Chrapkiewicz; Optics Letters, Vol. 40, Issue 7, pp. 1540-1543 (2015); DOI: http://dx.doi.org/10.1364/OL.40.001540

RELATED LINKS:

http://www.fuw.edu.pl/
Faculty of Physics at the University of Warsaw website.

http://www.fuw.edu.pl/informacje-prasowe.html
Press Office for the Faculty of Physics at the University of Warsaw.

MOVIES:

https://www.youtube.com/watch?v=BFIM5pHyd1k
For the first time, scientists from the Faculty of Physics at the University of Warsaw, Poland, have filmed individual photons forming pairs. (Source: UW Physics)

IMAGES:

FUW150422b_fot01s.jpg
HR: http://www.fuw.edu.pl/press/images/2015/FUW150422b_fot01.jpg
Under certain conditions, two individual, indistinguishable photons will form a pair as a result of interference. This subtle quantum effect has been successfully imaged for the first time by Micha? Jachura and Rados?aw Chrapkiewicz, doctoral students at the UW Faculty of Physics (both shown here, in multiple copies and grouped into pairs on both sides of the measuring apparatus). (Source: UW Physics, R. Chrapkiewicz)

FUW150422b_fot02s.jpg
HR: http://www.fuw.edu.pl/press/images/2015/FUW150422b_fot02.jpg
The vertical sequence of frames (bands) on the left presents two individual, distinguishable photons (green spots) appearing randomly together on one side, together on the other side, or on opposite sides of a beam-splitting plate (imaged in the middle of each band as a line separating the areas corresponding to the two sides of the plate). In the sequence of frames on the right, the two photons were indistinguishable and as a consequence were paired together. (Source: UW Physics)

[Attachments] See images for this press release:

Quantum 'paparazzi' film photons in the act of pairing up 2

ELSE PRESS RELEASES FROM THIS DATE:

The Association for Molecular Pathology compiles current research on liquid biopsy

2015-04-22

Bethesda, MD, April 20, 2015: The Association for Molecular Pathology (AMP), the premier global, non-profit organization serving molecular diagnostic professionals, today published a special article in The Journal of Molecular Diagnostics titled, "Do Circulating Tumor Cells, Exosomes, and Circulating Tumor Nucleic Acids Have Clinical Utility?" The report provides a thorough overview of research to-date on the minimally invasive "liquid biopsy" approaches to cancer diagnostics. "As a group of molecular diagnostic experts, we were intrigued and excited by the emerging ...

Hasbro Children's Hospital study links adverse childhood experiences to pediatric asthma

2015-04-22

Hasbro Children's Hospital study finds link between adverse childhood experiences and pediatric asthma Children who experience violence, substance abuse at home report significantly higher rates of asthma PROVIDENCE, R.I. - Robyn Wing, M.D., an emergency medicine physician at Hasbro Children's Hospital, recently led a study that found children who were exposed to an adverse childhood experience (ACE) were 28 percent more likely to develop asthma. The rate of asthma occurrence further increased in children with each additional ACE exposure. The study, recently published ...

Scientists watch living taste cells in action

2015-04-22

Scientists have for the first time captured live images of the process of taste sensation on the tongue. The international team imaged single cells on the tongue of a mouse with a specially designed microscope system. "We've watched live taste cells capture and process molecules with different tastes," said biomedical engineer Dr Steve Lee, from The Australian National University (ANU). There are more than 2,000 taste buds on the human tongue, which can distinguish at least five tastes: salty, sweet, sour, bitter and umami. However the relationship between the ...

More cars -- more traffic jams? Not for ants!

2015-04-22

Rather than slowing down, ants speed up in response to a higher density of traffic on their trails, according to new research published in Springer's journal The Science of Nature - Naturwissenschaften. When the researchers increased the supply of food by leaving food next to the trail, ants accelerated their speed by 50 percent. This was despite more than double the density of traffic. When food increases in supply, more forager ants are sent out to carry it back to the nest. With this increase in ant density, the number of encounters between outbound and incoming individuals ...

Surface matters: Huge reduction of heat conduction observed in flat silicon channels

2015-04-22

The ability of materials to conduct heat is a concept that we are all familiar with from everyday life. The modern story of thermal transport dates back to 1822 when the brilliant French physicist Jean-Baptiste Joseph Fourier published his book "Théorie analytique de la chaleur" (The Analytic Theory of Heat), which became a corner stone of heat transport. He pointed out that the thermal conductivity, i.e., ratio of the heat flux to the temperature gradient is an intrinsic property of the material itself. The advent of nanotechnology, where the rules of classical ...

New finding could help develop test for kidney disease

2015-04-22

Scientists at The University of Manchester have made an important finding that could help develop an early test for kidney disease. Dr Rachel Lennon from the Wellcome Trust Centre for Cell-Matrix Research has been studying why some people are more susceptible to kidney disease because of their race and gender. She explains: "It's well known that impaired kidney function is more common in Afro-Caribbean individuals compared to those from a Caucasian background, and in men compared to women. However, the reasons for the difference in susceptibility are only just being ...

Large heads, narrow pelvises and difficult childbirth in humans

2015-04-22

This news release is available in German. The size of the neonatal skull is large relative to the dimensions of the birth canal in the female pelvis. This is the reason why childbirth is slower and more difficult in humans than in most other primates. Scientists from the Universities of Oslo and Vienna, identified adaptations in the morphology of the human body, which were unknown so far. The results of this new study appeared in the current edition of PNAS. Upright walking and difficult birth In hominids, upright walking evolved 4-5 million years ago. The ...

The right programs can help college students suffering from depression, anxiety and stress

2015-04-22

Is it possible to prevent mental health problems in higher education students? The answer is "yes" according to a team of psychologists from Loyola University Chicago who conducted a careful, systematic review of 103 universal interventions involving over 10,000 students enrolled in 2- and 4-year colleges and universities and graduate programs. The findings appear in the May 2015 issue of Prevention Science, published by Springer. Researchers indicated that universal prevention interventions - that is, programs targeting general students, not just students who are at ...

Mindfulness-based therapy rather than antidepressants to prevent depression relapse?

2015-04-22

Researchers from Plymouth University Peninsula Schools of Medicine and Dentistry are part of a team led by the University of Oxford, who have carried out new research that suggests mindfulness-based cognitive therapy (MBCT) could provide an alternative non-drug treatment for people who do not wish to continue long-term antidepressant treatment. The results are published in "The Lancet". The results come from the first ever large study to compare MBCT - structured training for the mind and body which aims to change the way people think and feel about their experiences ...

Millimeter-sized stones formed our planet

2015-04-22

Fragments of asteroids regularly land on Earth as meteorites. If you examine such a find, you can see that it comprises millimetre-sized round stones, known as chondrules. These small particles are believed to be the original building blocks of the solar system. However, the research community has not previously been able to explain how the chondrules formed asteroids. A new study shows that asteroids were formed by capturing chondrules with the help of gravitational force. "The chondrules are of exactly the right size to be slowed down by the gas that orbited the young ...

One of the largest studies on preterm birth finds a maternal biomarker test significantly reduces neonatal morbidities and improves neonatal outcomes

One of the largest studies of its kind finds early intervention with iron delivered intravenously during pregnancy is a safe and effective treatment for anemia

[Press-News.org] Quantum 'paparazzi' film photons in the act of pairing up

Quantum 'paparazzi' film photons in the act of pairing up

ELSE PRESS RELEASES FROM THIS DATE:

LAST 30 PRESS RELEASES: