We investigate the range of validity of the recently developed steady-state ab-initio laser theory (SALT). While very efficient in describing various microlasers, SALT is conventionally believed not to be applicable to lasers featuring fully or nearly degenerate pairs of resonator modes above the lasing threshold. Here we demonstrate how SALT can indeed be extended to describe such cases as well, with the effect that we significantly broaden the theory's scope. In particular, we show how to use SALT in conjunction with a linear stability analysis to obtain stable single-mode lasing solutions that involve a degenerate mode pair. Our flexible and efficient approach is tested on one-dimensional ring lasers as well as on two-dimensional microdisk lasers with broken symmetry.

Self-assembled, epitaxially-grown InAs/GaAs quantum dots are promising semiconductor quantum emitters that can be integrated on a chip for a variety of photonic quantum information science applications. However, self-assembled growth results in an essentially random in-plane spatial distribution of quantum dots, presenting a challenge in creating devices that exploit the strong interaction of single quantum dots with highly confined optical modes. Here, we present a photoluminescence imaging approach for locating single quantum dots with respect to alignment features with an average position uncertainty < 30 nm (< 10 nm when using a solid immersion lens), which represents an enabling technology for the creation of optimized single quantum dot devices. To that end, we create quantum dot single-photon sources, based on a circular Bragg grating geometry, that simultaneously exhibit high collection efficiency (48 % +/- 5 % into a 0.4 numerical aperture lens, close to the theoretically predicted value of 50 %), low multiphoton probability (g(2)(0) <1 %), and a significant Purcell enhancement factor (~ 3).

Are you interested in studying the nature of light and how it interacts with nanoscopic bits of matter? We have a Ph.D. opening in our group, in the Physics Department in King’s College London.

The project combines network theory with nanophotonics, with the goal of studying how single emitters can be controlled and boosted in nanophotonic networks, towards quantum optics at the nanoscale.

For more information drop me an email: riccardo.sapienza AT kcl.ac.uk

 

 

Author(s): V. G. Sala, D. D. Solnyshkov, I. Carusotto, T. Jacqmin, A. Lemaître, H. Terças, A. Nalitov, M. Abbarchi, E. Galopin, I. Sagnes, J. Bloch, G. Malpuech, and A. Amo

Photons confined to a hexagonally shaped microcavity move in a polarization-dependent way, thus simulating a spin-orbit coupling common in materials.

[Phys. Rev. X 5, 011034] Published Wed Mar 25, 2015

Researchers show that a single photon can transfer an excitation from a quantum dot to an ion.

Published Mon Mar 23, 2015

Author(s): Alexey P. Slobozhanyuk, Alexander N. Poddubny, Andrey E. Miroshnichenko, Pavel A. Belov, and Yuri S. Kivshar

We suggest a novel type of photonic topological edge states in zigzag arrays of dielectric nanoparticles based on optically induced magnetic Mie resonances. We verify our general concept by the proof-of-principle microwave experiments with dielectric spherical particles, and demonstrate, experimenta…

[Phys. Rev. Lett. 114, 123901] Published Tue Mar 24, 2015

Author(s): H. M. Meyer, R. Stockill, M. Steiner, C. Le Gall, C. Matthiesen, E. Clarke, A. Ludwig, J. Reichel, M. Atatüre, and M. Köhl

Researchers show that a single photon can transfer an excitation from a quantum dot to an ion.

[Phys. Rev. Lett. 114, 123001] Published Mon Mar 23, 2015

Author(s): Mikolaj K. Schmidt, Javier Aizpurua, Xavier Zambrana-Puyalto, Xavier Vidal, Gabriel Molina-Terriza, and Juan José Sáenz

The polarization of the light scattered by an optically dense and random solution of dielectric nanoparticles shows peculiar properties when the scatterers exhibit strong electric and magnetic polarizabilities. While the distribution of the scattering intensity in these systems shows the typical irr…

[Phys. Rev. Lett. 114, 113902] Published Fri Mar 20, 2015

The only thing in science than may be even more prominent than the data deluge is the paper deluge: there is an increasingly large number of scholarly (and “scholarly”) journals, and an ever-increasing wealth of papers to fill them. Clearly, this calls for a paper to analyze the situation.

In a new study on the arXiv preprint server, a team of scientists at Aalto University School of Science in Finland and Hewlett Packard Enterprise Labs in California have examined the decay of attention in science.  To start their abstract, they write:

Full control over the dynamics of interacting, indistinguishable quantum particles is an important prerequisite for the experimental study of strongly correlated quantum matter and the implementation of high-fidelity quantum information processing. We demonstrate such control over the quantum walk—the quantum mechanical analog of the classical random walk—in the regime where dynamics are dominated by interparticle interactions. Using interacting bosonic atoms in an optical lattice, we directly observed fundamental effects such as the emergence of correlations in two-particle quantum walks, as well as strongly correlated Bloch oscillations in tilted optical lattices. Our approach can be scaled to larger systems, greatly extending the class of problems accessible via quantum walks. Authors: Philipp M. Preiss, Ruichao Ma, M. Eric Tai, Alexander Lukin, Matthew Rispoli, Philip Zupancic, Yoav Lahini, Rajibul Islam, Markus Greiner

Author(s): S. Roy, K. Ushakova, Q. van den Berg, S. F. Pereira, and H. P. Urbach

An optical microscopy scheme uses interference effects to reveal nanoscale defects on the surface of materials.

[Phys. Rev. Lett. 114, 103903] Published Thu Mar 12, 2015

Article

Colour change in many vertebrates originates from pigment dispersion or aggregation. Here, Teyssier et al . show that chameleons rapidly shift colour through a physical mechanism involving a lattice of nanocrystals in dermal iridophores, a second and deeper iridophore layer strongly reflects near-infrared light.

Nature Communications doi: 10.1038/ncomms7368

Authors: Jérémie Teyssier, Suzanne V. Saenko, Dirk van der Marel, Michel C. Milinkovitch

We have just published a new theoretical model including frequency interaction and mode competition in random lasing which allows to predict resonance-driven tuning of random lasing.   As it builds on solid previous models, we believe that it could be of practical use to predict the behavior of your random lasing system. If you are interested in the code just contact us.

Tuning random lasing in photonic glasses, Michele Gaio, Matilda Peruzzo and Riccardo Sapienza, Optics Letters 2015.
Abstract

Tuning random lasing in photonic glasses

We present a detailed numerical investigation of the tunability of a diffusive random laser when Mie resonances are excited. We solve a multimode diffusion model and calculate multiple light scattering in presence of optical gain which includes dispersion in both scattering and gain, without any assumptions about the β parameter. This allows us to investigate a realistic photonic glass made of latex spheres and rhodamine and to quantify both the lasing wavelength tunability range and the lasing threshold. Beyond what is expected by diffusive monochromatic models, the highest threshold is found when the competition between the lasing modes is strongest and not when the lasing wavelength is furthest from the maximum of the gain curve.

PDF available here: Tuning random lasing in photonic glasses

A mirror made with metamaterials reflects at a selected angle and only responds to radiation of a specific frequency, while being transparent to other radiation.

Published Fri Mar 06, 2015

Optics: Super vision

Nature 518, 7538 (2015). http://www.nature.com/doifinder/10.1038/518158a

Author: Zeeya Merali

Using techniques adapted from astronomy, physicists are finding ways to see through opaque materials such as living tissue.

Author(s): Carlo Manzo, Juan A. Torreno-Pina, Pietro Massignan, Gerald J. Lapeyre, Jr., Maciej Lewenstein, and Maria F. Garcia Parajo

Fundamental biological processes, including the capture of pathogens by membrane receptors, are regulated by molecular transport. Scientists show that receptor functioning is linked to nonergodic dynamics, which refers to the difference between the properties of a particle and an ensemble of particles.

[Phys. Rev. X 5, 011021] Published Wed Feb 25, 2015

Microwaves

I have had a particular problem for as long as I can remember. Any time I attempt to heat left over Chinese food in a microwave, it fails to heat completely through somewhere. Usually the center but not always and usually rice, but often it will be a small section of meat. It's baffling and has made me automatically adjust heating times to over 2 minutes. In most cases this tends to heat the bowl or plate more than the food. So I suppose the question is what is the optimal time to heat left over Chinese food in the microwave, how about an 800 watt microwave?

—James

This is a great question. Since the answer isn't too hard to find by Googling, normally I would skip it, but the answer is also something that I never really learned while growing up, so I'd like to try to answer it, for the sake of anyone else out there like me who spent years confused by microwaves.

First, the disclaimer: I am not an expert on food preparation or food safety. Actual experts on food safety can be found at US Department of Agriculture, which publishes a good FAQ page on microwave oven safety.

Now, on to James's question.

There are a couple of different effects that cause microwaves to heat food unevenly.

The first one is that microwaves have hot and cold spots. You can see this by filling a microwave with damp thermal paper, marshmallows, chocolate, or—possibly best of all—appalams.

The reason microwaves don't cook evenly comes straight from physics. When you continuously feed waves into a space—which is what microwaves do—you'll often have some "dead" spots:

In two dimensions, you get a similar but more complicated pattern.

These dead spots are the reason microwaves are designed with rotating platters—the idea is that each part of the food will pass through at least one hot spot. Microwave designers use a lot of tricks to try to vary the pattern to minimize dead spots, but no one does it perfectly; all microwaves will heat at least a little bit unevenly.

The second major reason for cold spots in microwaved food is something touched on in last week's article: Microwaves aren't absorbed very well by ice.

At first, this doesn't seem like a problem, right? It just means that if your food is partly or entirely frozen, you just need to microwave it longer. But when you do that, something interesting happens.

When ice melts, it turns to water,^{[citation needed]} which does absorb microwaves very well. When the first pockets of ice turn to water, they start absorbing more microwaves and heating very quickly, even though the ice around them hasn't even melted. Those melted parts can easily heat enough to start cooking the food while other parts are still frozen.

This means that if you defrost frozen meat in your microwave, it could be hot to the touch over most of its surface, but still have a solid chunk of ice in it somewhere. If it does, when you plop it on the stove,[1]Or in a pan on the stove, or whatever. the thawed parts might finish cooking before the frozen parts have even started to warm up, giving you a large chunk of raw meat in the middle of your steak.

This starts to explain some of the weird instructions commonly seen on microwavable food.

When instructions say let stand for 1-2 minutes, it's not just to protect your mouth from hot food—it's giving the hot and cold spots time to equalize, so the whole thing will be sufficiently heated throughout. And if some part of the food doesn't conduct heat well (e.g. rice) or contains a lot of chunks of ice (e.g. frozen fruit or meat) they also might tell you to stir midway through cooking. This helps to transfer the heat more evenly into the food, move food away from cold spots, and also break up chunks of ice and mix them with warmer pockets of water to help melt them.

This helps us explain why James is so perplexed. He's adjusting the obvious variable—total cooking time—and no matter what value he chooses, he's getting bad results.

The solution is to mess with other variables. First, he can redistribute the heat by pausing halfway through microwaving to stir the food. Second, for things that are harder to stir, he can give the heat time to equalize on its own. If he microwaves his food for a short period, waits a moment, then zaps it again, the heat will have time to spread from the hot spots to the cold spots in between zaps, resulting in more evenly-heated food.

And that brings us to one last surprising[2]This was surprising to me, anyway; I used microwaves for almost 20 years before I realized it. aspect of microwaves: Power level.

It turns out that "turning the microwave off every so often to let the food cool" is exactly what the "power level" setting does! Choosing a lower power level doesn't actually change the strength of the microwaves; it just means that the microwave generator won't be running the whole time. When you cook something on 50% power, you may notice the microwave's sound changing every so often; that's the dynamo turning on and off.[3]The length of these on/off periods (duty cycle) is surprisingly long, partly because switching off and on is hard on the magnetron. This is also the reason why, if you normally cook something for 2 minutes on 50% power, cooking it for 1:30 won't necessarily deliver 75% as much heat like you'd expect. While it's on, the microwave is running at full power. In effect, the microwave is just automating the tedious task of zapping something a bunch of times on "high" for 10 seconds each and letting it sit for a while in between.

So my advice to James is simple: Use a lower power level, stir your food partway through microwaving, and let it sit for a few minutes before you eat it.

And FYI, if you cut a grape in almost in half and microwave it, you'll create bursts of plasma. (You also might damage your microwave, so do it at your own risk.)

This has nothing to do with your question. I just wanted you to know.

Nature Physics 11, 105 (2015). doi:10.1038/nphys3229

Author: Christopher Jarzynski

Our framework for understanding non-equilibrium behaviour is yet to match the simplicity and power of equilibrium statistical physics. But recent theoretical and experimental advances reveal key principles that unify seemingly unrelated topics.