Quantum computation

A couple of days back, I received an interesting email from a rather curious mind.

The author of said email apparently found my contact details from one of the conference proceeding where I had submitted a paper.

Now, the author of the email posed rather curious questions, namely

…what exactly makes a quantum computer different from normal?…numerous articles point that quantum computer are superior because they can exist in two simultaneous states, but how does that exactly make a difference?…Lastly, every machine has its limits, so why is it being flaunted around as super machine?

Admittedly, given this was second email to me from a curious student so I was rather existed to answer it. Mind you, this person was also first one to continue conversations with follow up emails.

Anyways, while I did replied answers to all his questions, to the best of my abilities, it was later that I stumbled around this excellent article “What Quantum Computers Do Faster, with Caveats“. It is excellent articles that explains in short about the limitations of quantum computation. The author of this articles also uses Quantum Fourier Transform as example to explain the limitations.

One of the main idea about quantum world that I found hard to explain to him was that of superposition, something which he found surprisingly difficult to grasp; which may be attributed to his completely non-physics background.

When I had started to study about quantum information processing, I used to note down every interesting example or problem that would be capable of explaining a specific concept in a flash. Following is one of those noted example:

For example related to computer programming for understanding the superposition, one may look at a data structure called a linked list. Each data node in the list contains a pointer, to the next data node. The program traverses the list by jumping to the next data node indicated by the pointer. In a doubly-linked list, the data node contains two pointers, one for traversing to the top of the list, and another for traversing to the bottom of the list.

Another way of implementing a doubly-linked list is to use a single pointer space that contains the exclusive-or (XOR) or the two adjacent pointers. Figure below shows a link list node with pointer S that is the XOR of reference A (before) and reference B(after). To traverse the link list upward, the program XORs the current pointer (S) with the one it just left (B), and the result is the pointer of the next node (A). The same process works when traversing down the list. This superpositioning of node pointers is analogous to how the quantum states are maintained simultaneously in a quantum bit.

We can define those lists mathematically as follow:

 A = S \wedge B \uparrow


B = S \wedge A \downarrow


Earlier on, I also had bad habit of never noting down important points without due citation or source for the information. So credit for this example to original poster or author of blog post or paper, respectively. If anyone is aware of where this appears, kindly comment.

Lastly, there are two excellent articles on the Limits of Quantum Computers by Scott Aaronson here and here.


On the next Q+ Hangout

The next Q+ hangout is all set to run on 22nd April, 14:00 UTC+1. Surprisingly, the topic this time “On the Uncertainty of the Ordering of Nonlocal Wavefunction Collapse when Relativity is Considered”, which I had earlier read through and found to be highly interesting and no less entangled, no pun.

In the EPR experiment, if Alice makes a measurement on her particle then the state of Bob’s particle collapses to the result anti-correlated to Alice’s measurement. This process is said to be  happen instantaneously.

This ‘instantaneous’ gives rise to a paradox. For example, if in one reference frame Alice measures first then Bob’s state collapses. In a different inertial frame, an observer might say that Bob measured first leading to the collapse of Alice’s state. This leads to the identity paradox for who collapsed whose first!

This paper uses a type of clock device that functions on the laws of quantum-mechanics. This device in the experiment keeps the above paradox from occurring.

The bottom line being that in the experiment, Alice and Bob’s measurements cannot be made with infinite precision, rather they are constrained due to the energy-time uncertainty principle. Since energy and time are not relativistic invariant quantities, different observers in different reference frames must transform their uncertainty principles accordingly.

Concluding the paper rightfully claims the uncertainty principle in time always outruns the time difference induced by the change in reference frames. Neither Alice nor Bob will ever, with certainty, observe the two measurements swap temporal order. Furthermore, it can be said that  if a time measurement performed an entangled biphoton is simultaneous in one shared reference frame then it can be considered simultaneous to all measuring observers who do not share a reference frame.

On a personal note, it was only while going through the paper I thought about the time it takes for a EPR photon to collapse when measurement taken on its pair. People have already calculated it experimentally. This hangout already sounds like exciting, fingers crossed that I can attend it uninterrupted this time, have a couple of questions for the presenter.

Further Reading

On the Uncertainty of the Ordering of Nonlocal Wavefunction Collapse when Relativity is Considered arXiv:1310.4956 [quant-ph]

The Uncertainty Relation Between Energy and Time in Non-relativistic Quantum Mechanics DOI: 10.1007/978-3-642-74626-0_8

Experimental test of relativistic quantum state collapse with moving reference frames DOI: 10.1088/0305-4470/34/35/334

meQuanics – The Quantum Computing Game

Researchers from National Institute of Informatics(NII) have published a Web applications to advance the study of the quantum computer in the form of a game ‘meQuanics‘; previously called as “Qubit – the game“. It is basically a puzzle game where the puzzles are represented as circuit of the quantum computer. Each puzzle in meQuanics represents a real quantum algorithm. Even users who do not possess any knowledge of quantum mechanics can contribute to optimizing quantum circuits by solving the puzzles in the game. The stages/levels are divided into different circuits including : Shor, Josza, Bell, Muller and more.

The goal in the game is operating a ship that is loaded with quantum computer. If user can reduce the size of the puzzle that shows a quantum circuit, the speed of the ship is improved.

meQuanics is a project initiated in the Quantum Information Science Theory group (QIST) led by Prof. Kae Nemoto at the National Institute of Informatics (NII) in Tokyo, Japan. Dr. Simon Devitt and Prof. Nemoto conceived the idea during their ongoing research into large-scale quantum architecture design.

Currently meQuanics is provided as a Web application called trial version for now, but will be further developed as a fully integrated crowd sourced game for iOS, Android, Windows, MacOS and Linux platforms.

Here are some screenshots :

EDIT: For those who are curious in Quantum Algorithms visit : The quantum zoo

CFP: Seminar on the Philosophical Foundations of Quantum Gravity

26-28 September 2013 – University of Illinois at Chicago

Invited Speaker : Jeremy Butterfield (Cambridge), Bianca Dittrich (Perimeter Institute), Nick Huggett (UIC), Christian Wüthrich (UCSD), + others to be announced.

Dear colleague (apologies for mass mailing),

Chris Wüthrich and I are organizing a seminar on the foundations of quantum gravity, which will take place at the University of Illinois at Chicago from 26 to 28 September 2013.

The idea of this meeting is to bring together physicists and philosophers of physics interested in the foundations of quantum gravity (primarily canonical approaches and string theory), and to offer various formats such as keynote addresses, seminar-style talks, and sessions with contributed papers and works in progress.

Because the field is new, we are making efforts to make the meeting accessible to graduate students and recent PhDs with research agendas in quantum gravity (we hope to have some travel bursaries to help them attend, even if they do not present). In addition, we are especially keen to attract participation from women and minorities (whether or not junior).

We seek your help (a) to make sure that such people see the call for papers, and (b) to encourage them to submit work or attend.

To that end, please distribute this message to anyone that you think may be interested — hopefully with appropriate words of encouragement! If you have students or colleagues that you think we should know about, please give us their names, so that we can encourage them too. (Naturally you are also encouraged if the topic falls within your areas of research).

With gratitude,

Nick Huggett (UIC)
Christian Wüthrich (UCSD)

Quantum Gravity Seminar
9/26-28/13 – University of Illinois at Chicago

Email: beyondspacetimeseminar@gmail.com

Website: beyondspacetime.blog.com

The above quoted directly from quantum-foundations mailing list. For more information on it visit the blog.

Graham Farmelo on Paul Dirac and his concept of Mathematical Beauty

Adjunct Professor of Physics at Northeastern University in Boston, Graham Farmelo, on Paul Dirac and the Religion of Mathematical Beauty. Apart from Einstein, Paul Dirac was probably the greatest theoretical physicist of the 20th century. Dirac, co-inventor of quantum mechanics, is now best known for conceiving of anti-matter and also for his deeply eccentric behavior. For him, the most important attribute of a fundamental theory was its mathematical beauty, an idea that he said was “almost a religion” to him.


Google Scholar Manipulation and Boson Sampler

It is possible to manipulate the data and bibliometric indicators offered by Google product. Researchers from University of Granadas conducted experiment in which they created fake researcher and posted fake papers to inflate citation counts for the paper.

Manipulating Google Scholar Citations and Google Scholar Metrics: simple, easy and tempting 

On the quantum news, four papers have reported their research progress with experimental boson sampler. Check the papers below

On the same Scott Aaronson has posted excellent blog post titled ‘The Boson Apocalypse‘, in which he has a collection of all articles along with a small FAQ regarding the boson sampler, worth checking it out.

Simulation for Quantum Science [Part 3]

QCAD: Quantum circuit emulator

QCAD is a {surprisingly!} windows-based environment for quantum computing simulation which helps designing circuits and simulating them. Developed by Hiroshi Watanabe Masaru Suzuki and Junnosuke Yamazaki at University of Tokoyo and Nagoya University.

Extremely useful tool for designing Quantum circuits using graphical user interface (GUI). The designed cricuits can also be exported as EPS (Encapsulated Postscript) for use with LaTeX. I have not tried exporting the circuits but it does sound very useful.


Quantum Computer Emulator (QCE)

QCE is a software tool that emulates various hardware designs of Quantum Computers. QCE simulates the physical processes that govern the operation of a hardware quantum processor, strictly according to the laws of quantum mechanics. QCE also provides an environment to debug and execute quantum algorithms under realistic experimental conditions. The software consists of a Graphical User Interface (GUI) and the simulator itself. Developed and maintained by Zernike Institute for Advanced Materials, University of Groningen.

QCE runs smoothly on Windows XP and is known to support Windows 98/NT/2000/ME/XP environment. It gives a detailed exposition is given of the implementation of the CNOT and the To oli gate, the quantum Fourier transform, Grover’s database search algorithm, Shor’s algorithm, and more.

A paper titled “QCE: A Simulator for Quantum Computer Hardware” by K.F.L. Michielsen and H.A. De Raedt offers detailed information regarding QCE although the paper could have more clearer snapshots of the emulator in action.


jQuantum – Quantum Computer Simulation Applet

jQuantum is a quantum computer simulator. It simulates the implementation of quantum circuits on a small quantum register up to about 15 qubits. Its main intention is to create images—images which may help to learn and understand quantum circuits, and which perhaps will serve as building blocks for inventing new quantum algorithms. Hosted and supported by South Westphalia University of Applied Sciences.

Quantum Systems in Python

Recently read an extremely interesting post here by Markus Baden introduced to me the wonderful tool called Quantum Optics Toolbox in Python aka qutip. Developed by Robert Johansson and Paul Nation. It is truly the most marvelous tool, granted I just started to use it. The best thing is that one of the developer Robert Johansson has recently posted lecture notes for qutip. These notes contains ready to execute code which user can directly start playing with. Here are the notes in html format :

while the PDF of these are available on the github.

I am only disappointed that the latest version 2x and above wont be supporting windows officially.  Times like this make me happy that I am comfortable with Linux, though I still wish Mac prizes would drop down…

Quantum Games

I found this very interesting game, Quantum Chess. The goal of the game as opposed to normal chess is to capture the opposing king rather than checkmate. Other interesting thing about this chess is that when any piece lands on white square it remain in its ‘classical state’ but if it land on black square then it undergoes quantum transformation and regains a quantum superposition. It is pretty good game, though not the most educational, if I may say so.

Second interesting game is the Quantum Soccer. The goal of the game is for players to change potential energy surfaces to increase the probability of a quantum mechanical ball to be in the goal. Also the site has a nice text that narrates a story for the game here and the mathematical details here.

Lastly and my favorite is Quantum Minesweeper. Firstly you might want to start with the video tutorial before you play online. he game differs from classical Minesweeper in the following ways:

  • The board is really a quantum superposition of two boards. It is your goal to figure out the superpositions.
  • There are three different kind of measurements that you can do, each one a limited number of times. The measurements are :
  1. Classical measurement – collapse that can trigger a mine probabilistically. Very risky!
  2. Entropy measurement – it indicates if there is a superposition or not, but doesn’t tell you if there is a mine or not!
  3. Interaction-free measurements – doesn’t collapse the wave function, actually gives you the phase information.

This game is truly fantastic!! A must play.

Clearing the confusions of Weak Measurements

In the recent week there have been many reports like  Heisenberg uncertainty principle stressed in new test [BBC News], they are certainly very confusion for students, like me.

Thankfully an excellent post here pretty much clears all the confusion by systematically explaining everything. The post also has links to more of such articles in reputed journals.

Post on Quantum Bayesian Networks