Science AMA Series: I'm Dr. Jelena Vuckovic, Professor of Electrical Engineering at Stanford University and Fellow of The Optical Society (OSA). I do research on nanophotonics, quantum optics, nonlinear optics, quantum information technologies and optoelectronics. Ask Me Anything!

Abstract

In my daily position, I am a Professor of Electrical Engineering and by courtesy of Applied Physics at Stanford University, where I lead the Nanoscale and Quantum Photonics Lab in the Ginzton Laboratory. After completing my PhD in Electrical Engineering from the California Institute of Technology (Caltech) in 2002, I worked as a postdoctoral scholar at Stanford. In 2003, I joined the Stanford Electrical Engineering Faculty, first as an assistant professor (until 2008), then an associate professor with tenure (2008-2013), and finally as a professor of electrical engineering (since 2013). As a Humboldt Prize recipient, I also have a visiting position at the Institute for Physics of the Humboldt University in Berlin, Germany (since 2011). In 2013, I was appointed as a Hans Fischer Senior Fellow at the Institute for Advanced Studies of the Technical University in Munich, Germany. I am honored to be a Fellow of The Optical Society (OSA) and the American Physical Society (APS).

I'll be back at at 3 pm ET to answer your questions, ask me anything!

Thank you for the AMA. I hope this is within your purview. What is holding back quantum computing? Is there a particular aspect of it that, if overcome, could open up the technology?

prodigies2016

Quantum mechanical systems are very fragile. To preserve quantum mechanical properties, they have to be very well isolated from the environment, and this is very, very challenging. This is especially true for a quantum computer, where we need a large number of entangled quantum objects. I think that at the moment, the superconducting platform for implementation of quantum computers is ahead relative to the other approaches (please see for example the work done by Schoelkopf and Devoret at Yale, and also by Martinis at UCSB/Google, in addition to many other places). The drawback of superconducting systems is the lack of a good optical interface, which would be important for a quantum internet, but people are working hard on microwave to optical quantum frequency conversion. While the first functional quantum computer may likely be superconducting circuits based, I also think that we have yet to discover materials that would be most suitable for practical quantum computing systems. The research on color centers in semiconductors that I described I another reply is potentially very promising, because of the small inhomogeneous broadening, decent coherence times, and their potential for scalability and even room temperature operation.


Pozdrav Jelena.Zaista mi je drago sto je neko iz nase zemlje,i to jos iz mog grada uspeo tako daleko da dogura. Sta mislis o stanju nauke u Srbiji? Prevashodno mislim na teoriju,zato sto znam da je jako,jako,jako tesko da se nadje para za bilo kakav eksperiment.Da li ima bilo kakvog pomaka ili napretka sto se tice tehnickih nauka?

Greetings Jelena (it's pronounced "yɛ-lɛ-nah" people, like Y in YES, not like J in JEANS!!!) . I am really glad to see that somebody from our country, and from my city nonetheless, has made it so far What is your opinion on the state of science in Serbia? Primarily i am referring to theory,because i know that is really,really,really difficult to find any money for an experiment.Is there any progress regarding natural/physical science?

BaldrickMate

Hvala (thanks)! I am aware of the strong, ongoing theory research in my field taking place at the Institute for Physics and in Vinca in Belgrade. They also organize an international conference called Photonica that I attended a few years back, where I learned more about their efforts.


How far are we from meta lenses that could be truly usable in a modern microscopy context? As someone who primarily deals with super-resolution microscopy on a daily basis I find the field fascinating, but notice that a lot of my peers are extremely skeptical that meta lenses could offer good optics solutions, especially in terms of things like chromatic aberration.

whiteknight521

I don't work on lenses at the moment, but my former PhD student Andrei Faraon (now a faculty at Caltech) has been doing some very exciting work on thin lenses based on meta surfaces - please check it out. Indeed, chromatic aberrations are an issue, but there may be solutions there - with multilayer systems, or maybe even by employing our inverse design approaches to design thin lenses without chromatic aberrations. We have been thinking about this a little bit. If you are interested in learning about inverse nanophotnic design, here are some of our recent papers: Silicon Photonics: Design approach to integrated photonics explores entire space of fabricable devices, Alexander Y. Piggott, Jesse Lu, and Jelena Vučković, Laser Focus World, 52 (3) (2016) Inverse design and demonstration of a compact and broadband on-chip wavelength demultiplexer, Alexander Y. Piggott, Jesse Lu, Konstantinos G. Lagoudakis, Jan Petykiewicz, Thomas M. Babinec, and Jelena Vučković, Nature Photonics 9, 374–377 (2015) Nanophotonic computational design, Jesse Lu and Jelena Vuckovic, Optics Express Vol. 21, 11, pp. 13351-13367 (2013)

If you are referring to super lenses based on negative index metamaterials: I have not been following that work very closely, but as far as I know, the main limitations come from metal losses.


1) What have you been working on lately?

2) What are potential applications of your work?

3) Is there any potential for optical computing, neuromorphic or otherwise?

georgeo

1) I have already described some our ongoing projects on this AMA, but let me pick two to highlight here: multi emitter cavity QED with color centers in diamond and silicon carbide, and inverse design and implementation of nanophotonic structures. I wrote more about both of these projects in other replies so please check that out.

2) The most immediate application is in optical interconnects that I have also discussed already in reply to another question. In addition, there are potential applications in medicine (both for sensors or X-ray sources), optics communications, and maybe the longest shot of all in long distance quantum networking and quantum computing.

3) In general purpose computers, the pressing issue is not really in gates, but in interconnects which are very inefficient, particularly at high operating speeds. This is why the first place where optics will be used inside of computers is in optical interconnects that I discussed in another reply. While an all optical general purpose computer is a more distant future, I believe that we will see more use of optics to solve specific problems - essentially equivalent to analog, special purpose computing. Having this said, we are working actively on developing attojoule, high speed optoelectronics that could potentially be used in scalable optical gates for general purpose computers (please see our multi-university research program on this topic led by Prof. Andrea All at UT Austin, funded by AFOSR and managed by Dr. Gernot Pomrenke: http://afosr-muri-alu.ece.utexas.edu)


I would love to have your opinion on a renewable energy related question.

When do you think Graphene will be used in Solar Panels and do you think that aqueous, polymer based batteries are the future?

Thanks in advance, from a boy trapped in a mans body :)

lanzasub

A much better person to answer this question is prof. Yi Cui from Materials Science Department at Stanford (since I don't work on these problems).


Why do quantum dots blink?

notinsanescientist

I work with epitaxial quantum dots (InAs/GaAs) grown by MBE that tend to blink less than colloidal (chemically synthesized) quantum dots. Blinking is result of defects and growth imperfections (charge traps, nearby impurities, surfaces) which lead to quantum dot getting trapped in a dark state part of the time. Higher purity MBE growth generally leads to higher quality quantum dots that blink less. I also know that chemists are working hard on developing the right type of shells for colloidal quantum dots, to minimize blinking. When I was a postdoc, we did some extensive studies of blinking in InAs/GaAs quantum dots. In case you are interested in details of physics, our paper is posted on my group's website: Sub-microsecond correlations in photoluminescence from InAs quantum dots, C. Santori, D. Fattal, J. Vuckovic, G. Solomon, E. Waks, and Y. Yamamoto, Physical Review B, vol. 69, article 205324 2004


How far is optical computing and what are problems with it?

kotokot_

I just answered the same question above, so I will copy a part of my reply below.But let me first emphasize that there is really no reason to replace electronics with optics, unless there are benefits in terms of reduced energy consumption and increased speed. There are clear gains in replacing electrical with optical interconnects, but not yet in optical gates. Scalability of optical gates is another issue. And here is a copy of what I wrote in another reply:

In general purpose computers, the pressing issue is not really in gates, but in interconnects which are very inefficient, particularly at high operating speeds. This is why the first place where optics will be used inside of computers is in optical interconnects. While an all optical general purpose computer is a more distant future, I believe that we will see more use of optics to solve specific problems - essentially equivalent to analog, special purpose computing. Having this said, we are working actively on developing attojoule, high speed optoelectronics that could potentially be used in scalable optical gates for general purpose computers.


What's the next step in photonic crystals and/or their computer applications?

ng12ng12

For many applications, we have realized that periodic structures and regular geometric shapes like photonics crystals may not be the optimal solutions. Recent advances in nanophotonic design have led to developments of some highly non-intuitive designs that outperform photonics crystals, or other traditional optical structures (please see my replies discussing inverse nanophotonic designs). Therefore, I will answer your question more broadly: what is the next step in computer applications of nanophotonics? I believe it is in optical interconnects. I already talked about this in another reply, but here is the main story: optical interconnects are replacing copper wires inside of computers with optical links. We already have building blocks for this (efficient, high speed sources, detectors, modulators, as well as waveguides), but they also need to have small footprints, to be robust to temperature variations and fabrication imperfections, and to be fully compatible with silicon electronics platform. We and many others are working on addressing these issues. Putting all of the building blocks together in an efficient way would dramatically decrease energy consumption in computers and data centers resulting from inefficient electrical interconnections, while increasing the operating speed. Prof. David Miller from Stanford has an excellent review paper on optical interconnects explaining all of this in detail.


Thank you for doing an AMA!

What are some potential applications of nanophotonic and quantum optic technologies? How feasible is it to scale up production of these materials? Are there established disposal protocols/regulations for metallic nanoparticles?

shiruken

I think the most immediate application would be in optical interconnects - replacing copper wires inside of computers with optical links. We already have building blocks for this (efficient, high speed sources, detectors, modulators, as well as waveguides), but they also need to have small footprints, to be robust to temperature variations and fabrication imperfections, and to be fully compatible with silicon electronics platform. We are working on addressing these issues. Putting all of the building blocks together in an efficient way would dramatically decrease energy consumption in computers and data centers resulting from inefficient electrical interconnections, while increasing the operating speed.  As for disposal protocols for metallic nanoparticles - I don't work with them, but I do know that there is a lot of ongoing research on the health effects of these and other nanoparticles. Prof. Sam Gambhir at Stanford is one of the leading people in the field - please check his work.


What are your thoughts on the rapid rise of fiber lasers and doped fiber amplifiers? Are photonic crystal systems (e.g. Ti:Sapphire) becoming obsolete?

Just for fun: What is the shortest laser pulse utilized in your lab? What is the highest peak power? What is the most dangerous laser?

shiruken

I don't work on development of fiber lasers, fiber amplifiers, and OPO systems, but there is a lot of effort at Stanford in these areas (please check the work of Professors Michel Digonnet, Bob Byer, and Marty Fejer). My research is focused on building low power and high speed devices and systems, which means that we don't really employ high power lasers in our work. But we have a few Ti:sapphire systems in the lab, and the shortest pulses we use are on the order of 100fs. The excitation powers we use are generally in the microwatt range, and we attenuate lasers before exciting the structures. If you are wondering about the timescales of the fastest processes that we study - they are on the order of few 10's of ps.


Hi! Thanks for the AMA. I have a couple questions,

1) I am curious as to what your thoughts are on using color centers as quantum memories.

2) I see on your website, that you are "demonstrating solid state multi-emitter cavity QED". I am curious how you do that. When i think cavity QED, my mind often jumps to the JC picture, but it sounds like you make cavities within your crystals. Is this correct?

3) I think your work is really interesting. What are the prospects of a postdoc in your group in 3-4 years? :)

Thanks again

hbar340

  1. There is a lot of ongoing research on color centers, as you may know. For quantum memories, a good coherence time and a good photonics interface are critical. Some of the currently studied color centers have good coherence times, but optical interfaces are challenging, because these color centers are sensitive to nearby surfaces (e.g., NV center in diamond). Other centers like SiV in diamond are less sensitive to nearby surfaces in optical structures, but have shorter coherence times (although this may be improved by some careful and smart engineering). I think that the ongoing research looking into various color centers in group IV materials and rare earth doped crystals is very exciting, and that the best material for quantum memories is yet to be identified. Nevertheless, there is a lot of potential for color centers beyond quantum memories - for example in optical switching devices, or quantum light sources (neither of these require long coherence times).

  2. I already answered another question on multi-emitter CQED , but here is a copy of that reply. We are very interested in multi-emitter cavity QED systems, where several emitters are collectively strongly coupled to a cavity. Here is our recent theory work, and we are working on the experimental demonstration of these effects on the diamond color-centers platform (where inhomogeneous broadening of quantum emitters is very small): Nonclassical Light Generation in Two-Emitter-Cavity Systems, Marina Radulaski, Kevin A. Fischer, Konstantinos G. Lagoudakis, Jingyuan Linda Zhang, Jelena Vuckovic. (arXiv:1612.03261) Nonclassical Light Generation from III-V and Group-IV Solid-State Cavity Quantum Systems, Marina Radulaski, Kevin Fischer, Jelena Vučković. (arXiv:1701.03039)

  3. Thank you for your interest in my group! Please feel free to contact me when the time for a postdoc approaches, and keep doing good research in the meantime. :)


Hello Professor. I'm an undergrad electrical engineering student who had a rough start in my academic career (albeit at one of the nations top institutions) but would still like to go to graduate school. What is something that a second year student with a low CGPA can do at this point to increase my chances of being considered for acceptance?

phwak

I would advise you to get involved in research as soon as possible. Strong research experience during your undergrad is significantly increasing your chances of admission to a graduate program. Good luck!


Hi there, Chemistry undergrad working in a Terahertz/Ultrafast spectroscopy lab interested nano-photonics. Question: How have your research interests evolved over your career? Did you always have an interest in nano-scale electronics? I'm hopefully about to begin graduate work--I'm assuming that many scientists see their primary interests change or significantly evolve over their career. Given that assumption what skills do you think are important to develop--that have helped you over your career?

chemoses

Indeed, your research interests may change a lot over time. I started grad school at Caltech with a primary interest in information theory, but then decided to work on nano photonics and quantum optics. I find that any research experience from your undergrad years is beneficial for quickly ramping up your research later, as a PhD student, because you learn that doing research is very different from doing homework, and that there is no always (quick) solution to the problem you are solving. For the work that I do, strong background in physics and math is certainly very important. I hope this helps and good luck with your career!


Hello Dr. Vuckovic, thanks for taking the time to come talk with us about your research.

I read the abstract of the paper your lab recently published and hate to admit that I wasn't able to make much sense of it, since I lack a lot of the requisite knowledge.

What are CQED and could you give an overview of how the light-matter interface works and what it allows you to do? Thanks!

PapaNachos

Thank you for your interest in my work. Here is a link to the book chapter I wrote recently, which is based on the lectures I gave at the Nanophotonics and quantum optics summer school in Les Houches, France: Quantum optics and cavity QED with quantum dots in photonic crystals, Jelena Vuckovic (arXiv:1402.2541). Lectures given at Les Houches 101th summer school on “Quantum Optics and Nanophotonics", August 2013 (to be published by Oxford University Press) Reading this chapter before reading our articles would most likely help you. It also gives an introduction into cavity QED (in addition to photonics crystals and quantum dots). I hope this helps and good luck!


I have studied optoelectronics in my master's program however I may remember little and be of the mark. Specifically the use of gold nano particles self assembling into chains capable of transmitting information using plasmonics. The plasmonic effect is close to the photonic, with chains being excited by light and should chains intersect, interferometric logic can be performed. Using this effect it is possible to design all of the standard logic gates and perform transistor like operations purely in plasmonics using only light. The switching speed of these gates is the speed of light. Have you heard anything about this phenomenon and can you comment on how/when it could find its way into consumer electronics?

Jigabit

I believe that you refer to the plasmonics work on metallic nanoparticle chains which was pioneered at Caltech in the group of Prof. Harry Atwater (the people involved with it were also Prof. Mark Brongersma now at Stanford and Prof. Stefan Maier now at Imperial College). Indeed, there are many exciting opportunities with metals because of the strong optical field confinement. Unfortunately, they are extremely lossy at optical wavelengths, and are a good choice only for applications where you can tolerate large loss. My research group focuses primarily on nano photonics with dielectrics for this reason. You may also be interested in my reply to another question above on optical interconnects.


How close are we to holograms?

karakatsu

I don't work in this field, but I am familiar with an exciting ongoing work in Leia 3D - a company founded by David Fattal with whom I worked closely while he was a PhD student at Stanford.


Do you have plans to write an academic book on nanotechnology and nanomaterials like H.-S. Philip Wong and other academics in Stanford University?

Mundanus

I have been thinking about writing a book, but unfortunately, haven't had time to do it. So far, I wrote several book chapters, some of which you can download from my website. And I also wrote course readers for the classes that I teach at Stanford (optical micro cavities - EE340, and intro to nano photonics and nanostructures - EE136), which could eventually be turned into a book.


Is Electrical Engineering Better than Mechanical Engineering?

Blavkmanfooh

Of course it is! :)

Now seriously: if you are asking whether to study Electrical or Mechanical Engineering, I believe that both of these fields are very promising and have excellent job prospects.


Good afternoon Professor, thanks for doing this AMA.

How has modern nanofabrication and optical design techniques allowed you to localize photons to sub-wavelength volumes?

milrey76

Localizing photons efficiently (for a long time and in a small volume) requires sophisticated optical structure designs. We used to rely on structures consisting of regular, geometric patterns (such as photonic crystals, rings or disks), but recent advances in optical design indicate that those may not be optimal solutions, and we (and others) have been developing some highly non-intuitive designs. In any case, resulting structures have small, sub-wavelength features and therefore, their implementation relies on the modern nanofabrication methods.


Good evening!

Undergrad Mat.Eng student here, thinking about internships and the future. I find ceramics the most interesting materials, specifically optical and electrical properties and energy applications.

So; Have you worked with companies (e.g Corning) in the past? What did you work on?

What inspired you as an undergrad?

Thanks for doing this AMA! All the best

Yeah_Chons

While I was a PhD student at Caltech, we had a collaboration with Corning on photonics crystal waveguides. Here is our paper, if you are interested: Experimental and theoretical confirmation of Bloch-mode light propagation in planar photonic crystal waveguides, M. Loncar, D. Nedeljkovic, T. P. Pearsall, J. Vuckovic, A. Scherer, S. Kuchinsky, and D. C. Allan, Applied Physics Letters, vol. 80, No. 10, pp. 1689-1691, 2002. I also know some recent Stanford photonics graduates who went to work for Corning. Good luck with your internship!


What are some interesting problems in quantum optics and nano photonics that your lab is planning to tackle in the future? And why did you pick those problems?

not_a_theorist

We are very interested in multi-emitter cavity QED systems, where several emitters are collectively strongly coupled to a cavity. Here is our recent theory work, and we are working on the experimental demonstration of these effects on the diamond color-centers platform (where inhomogeneous broadening of quantum emitters is very small): Nonclassical Light Generation in Two-Emitter-Cavity Systems, Marina Radulaski, Kevin A. Fischer, Konstantinos G. Lagoudakis, Jingyuan Linda Zhang, Jelena Vuckovic. (arXiv:1612.03261) Nonclassical Light Generation from III-V and Group-IV Solid-State Cavity Quantum Systems, Marina Radulaski, Kevin Fischer, Jelena Vučković. (arXiv:1701.03039)

I am also very excited about our continuing efforts on inverse nanophotonic design, where we use optimization methods to design and implement nanopohotonic devices with better performance relative to state of the art (smaller footprint, robust, higher efficiency etc). We are now also a part of the large international collaboration led by Prof. Bob Byer at Stanford (and supported by the Moore foundation) which is focused on developing on chip laser driven particle accelerators. My group employs the aforementioned inverse design approach to design optical structures for this accelerator. If you are interested in learning more about our inverse nano photonics design, here is one reference: Inverse design and demonstration of a compact and broadband on-chip wavelength demultiplexer, Alexander Y. Piggott, Jesse Lu, Konstantinos G. Lagoudakis, Jan Petykiewicz, Thomas M. Babinec, and Jelena Vučković, Nature Photonics 9, 374–377 (2015)

I picked those problems because they are very exciting to work on, and also rely on a number of interesting tools: optimization techniques (and machine learning), modern nano fabrication, and fun nano photonics / optics experiments. But at the same time, they also have a great application potential - such as optical interconnects that I discussed in another reply here, or compact X-ray sources for medicine.


What is your opinion on the differences between Engineering and Engineering Technology? I have seen a lot of arguments back a forth as to the worth of each and if engineering technology is treated as a real engineering education.

Currently as a power plant operator I make more than the engineers at my plant so going back to school for more money isn't really a need. I take classes online for Electrical Engineering Technology mostly because it is challenging to me an with my rotating work schedule online school is my best option. The program I am taking is ABET accreditation for engineering technology.

kbilly1

I am not familiar with specific programs you mention, but I think that Electrical Engineering may be broader than Engineering Technology (there is a lot of science in Electrical Engineering, to prepare students for graduate education). Good luck with your continuing education!


Thank you for taking the time to answer questions here! I have one final question. Could you share your personal worldview regarding science? What keeps you motivated to do research and do you have some end goal in mind?

not_a_theorist

I enjoy the process of scientific discovery: asking yourself a question, and then devising a method or an apparatus to answer that question. And in the part of research spectrum where I work, it is truly fascinating to observe the behavior of the world on the nano-scale and in the quantum domain. Doing research is a lot of fun, but also very rewarding: not only because we provide answers to the fundamental questions of the Nature, but also because we can use our findings to address great technological challenges of our world (such as reducing energy consumption in computing that I discussed here). Research is unpredictable and it is difficult to set up one fixed end-goal far ahead in the future. I prefer to work towards intermediate goals, and to be flexible with defining them. And by intermediate goals I don't mean to work on lower impact research: instead, I prefer to break my research trajectory into shorter routes that are easier to chart and achieve.


What are some real life application of the Laplace Transform?

todayIact

In optics, we use Fourier transforms a lot, and Laplace transforms are used in designing control systems. Those engineering classes on transforms end up being quite useful, indeed.


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