New paper: Detection loophole closed using photons

A new paper just appeared on the arxiv that claims to close the detection loophole (also known as the fair-sampling loophole) in Bell's Inequalities. If this is true (and from a first reading it appears they have a solid case) it is another important step along the way to a loophole free test of Bell's inequalities. This makes photons the first system in which all loopholes have been closed independently. Now the (even more) difficult task of a loophole free experiment begins.

Once the paper goes through the peer review process I will try and post a more detailed write up about the results. In the meantime, grab the preprint from the arxiv. Congratulations to all those involved!

Here is the abstract:

The violation of a Bell inequality is an experimental observation that forces one to abandon a local realistic worldview, namely, one in which physical properties are (probabilistically) defined prior to and independent of measurement and no physical influence can propagate faster than the speed of light. All such experimental violations require additional assumptions depending on their specific construction making them vulnerable to so-called "loopholes." Here, we use photons and high-efficiency superconducting detectors to violate a Bell inequality closing the fair-sampling loophole, i.e. without assuming that the sample of measured photons accurately represents the entire ensemble. Additionally, we demonstrate that our setup can realize one-sided device-independent quantum key distribution on both sides. This represents a significant advance relevant to both fundamental tests and promising quantum applications.

GoldieBlox: Engineering toys for girls

Debbie Sterling decided it was time to make engineering toys that appeal to girls, so she founded a new kind of toy company called GoldieBlox. Her Kickstarter campaign was fully funded in 5 days. This observation of hers struck me:

How do you get girls to like a construction toys? It all came down to one simple thing: boys like building and girls like reading.

You can pre-order the toys now with the first deliveries set for April 2013.

Entangling three photons in energy and time

Entangling three photons in energy and time

Our latest paper, on which I was the lead author, has just been published in Nature Physics. I am working with Jasper Palfree to develop a comprehensive page that explains the work. Unfortunately, that is not ready yet. In the mean time, here is the official press release:

Photon Triplet Counts

Extending Einstein

Researchers at the University of Waterloo and the University of Calgary have carried out an experiment, using the quantum properties of three particles light, that could provide new insights into the philosophical arguments by Einstein about the foundations of quantum mechanics.

In 1935 Albert Einstein, Boris Podolsky, and Nathan Rosen (EPR) published a thought experiment designed to show that quantum mechanics, by itself, is not sufficient to describe reality. Using two entangled particles – particles that share correlations stronger than those allowed by classical physics – EPR tried to demonstrate that there must be some hidden parameters that quantum mechanics does not account for. The ensuing debate led to the pioneering work of John Bell who, in 1964, showed that by following the arguments of EPR to their logical conclusion one arrives at a contradiction with experiments; hidden parameters, like the ones EPR argued for, are incompatible with our observations of nature and the mystery at the heart of quantum mechanics remains intact. This has profoundly shaped our understanding of quantum theory, and today the entanglement between two particles that EPR first proposed is a valuable resource in emerging quantum technologies like quantum computing, quantum cryptography, and quantum precision measurements.

77 years after EPR's landmark work a new paper in Nature Physics, authored by physicists at the Institute for Quantum Computing in Waterloo and at the University of Calgary, has finally experimentally extended the original ideas of Einstein and his colleagues from two to three entangled particles. This new form of three-particle entanglement, based on the position and momentum properties of photons, may prove to be a valuable part of future communications networks that operate on the rules of quantum mechanics, and could lead to new fundamental tests of quantum theory that deepen our understanding of the world around us. According to group leader Thomas Jennewein, "It is exciting, after all this time, to be able to create, control, and entangle quantum particles in this new way. Using these states of light it may be possible to interact with and entangle distant quantum computer memories based on exotic atomic gases."

In the experiment the researchers took a highly energetic blue photon and passed it through a special crystal that caused it to split into a pair of red coloured daughter photons. They then repeated this process with one of the daughter photons to create three entangled photons. The energy of these three photons, through the conservation of energy, must be equal to the energy of the original blue photon. Because the splitting process is instantaneous, the three photons must arrive at the detectors at the same time. It is therefore possible to learn the precise energy (corresponding to their total momentum) of the three photons as well as their arrival times (corresponding to their position). At first this seems to be an apparent contraction with the Heisenberg uncertainty principle which states that it is impossible to simultaneously learn arbitrarily precise information about a particle's position and momentum. However, with entangled particles, it is possible to gain precise information about the sum and differences of their position and momentum in a manner not possible with classical particles. This is in part because each of the particles in an entangled state gives up its own individual identity–the properties of the particles are instead shared collectively. It still remains impossible to gain position and momentum information of any individual particle. Says lead author Krister Shalm, "It is as if you could only discover how many points two teams combined to score in a basketball game, but had no way of knowing how many points each individual team had scored." Co-author Deny Hamel adds, "Because the entangled photons cooperate with one another they can do things that classical particles are unable to."

The next step for the researchers is to try to combine the position and momentum entanglement between their three photons with more traditional types of entanglement based on angular momentum. This will allow the creation of hybrid quantum systems that combine multiple unique properties of light at the same time. According to Christoph Simon from the University of Calgary, "This work opens up a rich area of exploration that combines philosophy, quantum mechanics, and quantum technologies. The powerful insights by Einstein and his co-workers in 1935 are still informing the way we understand the world around us."

Getting your paper rejected may lead to it having a higher scientific impact

Philip Ball reporting for Nature News on a new study about the scientific impact of papers that are initially rejected:

Just had your paper rejected? Don’t worry — that might boost its ultimate citation tally. An excavation of scientific papers' usually hidden prepublication trajectories from journal to journal has found that papers published after having first been rejected elsewhere receive significantly more citations on average than ones accepted on first submission.

The peer-review process is far from perfect, but I feel that every paper I have been involved with has improved as a result of the referee comments. It can be frustrating at times, but the quality of a manuscript can dramatically increase with the (mostly) useful feedback reviewers provide.

2012 Nobel Prize: How Do We See Light?

Henry Reich from Minute Physics explains the science behind Serge Haroche's quantum non-demolition measurements. Since Max Planck and his study of black body radiation, the interaction between light and matter has played a critical role in the development of quantum mechanics.

Haroche's experiment was able to detect, without destroying, the presence of single photons in a cavity cooled to 0.8K. This allowed him to "see" the birth and death of black body radiation photons. Being able to detect single photons without destroying them has important implications for quantum information. I have always been taken by how this experiment connects Planck's work with quantum information, forming a beautiful narrative that spans more than a century of physics. This is only one of several incredible experiments by Haroche that contributed to his selection for the 2012 Nobel Prize in physics.

I am also continually amazed by Henry and the quality, both in presentation and content, of his videos.

A way around Nobel’s 3-person limit

It is rare for a discovery or breakthrough in science to come from a single person or group. Science is a collaborative effort so how do you appropriately give credit for a discovery with something like the Nobel Prize where many people have contributed, but only up to three people can be recognized? Charlie Bennet has a clever solution using randomness.

Quantum Optics Researchers win 2012 Nobel Prize

Quantum Optics Researchers win 2012 Nobel Prize

David Wineland And Serge Haroche
David Wineland And Serge Haroche

From the Nobel Prize Committee:

The Nobel Prize in Physics 2012 was awarded jointly to Serge Haroche and David J. Wineland "for ground-breaking experimental methods that enable measuring and manipulation of individual quantum systems"

This is exciting news for people, like myself, who work in the field of quantum optics and quantum information. Both David Wineland and Serge Haroche have spent decades carrying out beautiful experiments that further push and refine our ability to manipulate and control quantum systems.

David Wineland's work with trapped ions has led to important improvements in atomic clocks and served as exciting testbed for quantum computing. Serge Haroche's work with cavity quantum electrodynamics is opening up new techniques for controlling the interaction of light and matter.

The Nobel Prize Committee has a nice, but slightly more technical, background of the research that is worth a read:

The behaviour of the individual constituents that make up our world – atoms (matter) and photons (light) – is described by quantum mechanics. These particles are rarely isolated and usually interact strongly with their environment. The behaviour of an ensemble of particles generally differs from isolated ones and can often be described by classical physics. From the beginning of the field of quantum mechanics, physicists used thought experiments to simplify the situation and to predict single quantum particle behaviour.

During the 1980s and 1990s, methods were invented to cool individual ions captured in a trap and to control their state with the help of laser light. Individual ions can now be manipulated and observed in situ by using photons with only minimal interaction with the environment. In another type of experiment, photons can be trapped in a cavity and manipulated. They can be observed without being destroyed through interactions with atoms in cleverly designed experiments. These techniques have led to pioneering studies that test the basis of quantum mechanics and the transition between the microscopic and macroscopic worlds, not only in thought experiments but in reality. They have advanced the field of quantum computing, as well as led to a new generation of high-precision optical clocks.

Here is an interview with David Wineland that IQC conducted earlier this year when he was visiting.

Congratulations to both research groups and everyone involved.

Beautiful Chocolate

Beautiful Chocolate

Beautiful Chocolate Bars by Anna Tolazzi

This weekend at the farmers' market Jaime and I bought some amazing chocolate from a local chocolatier, Anna Tolazzi. I was taken by how beautiful the wrappers were on each bar. The chocolate is made from high-quality fair-trade organic ingredients, and is made locally. I was excited by the wrappers while Jaime was excited by all the vegan options, and we ended up buying five different bars to try.

Beautiful Chocolate: Salted Caramel

####Salted Caramel#### This bar is my favourite, and not just because the wrapper is covered in random physics equations. The chocolate is not very sweet, but the caramel inside is homemade and balances the dark chocolate nicely. A few seconds after the first bite the salt kicks in.

Beautiful Chocolate: Passion fruit, mango, and coconut  semi-sweet chocolate

Passion fruit, mango, and coconut semi-sweet chocolate (Vegan)

Normally I only like chocolate this dark if it has a strong mint flavour. Here the passion fruit, mango, and coconut are very subtle, but the chocolate does not taste bitter. Very subtle and refined.

Beautiful Chocolate: Wild Blueberries and Earl Grey Tea

####Wild Blueberries and Earl Grey Tea (Vegan)#### I am a big Earl Grey tea fan. Watching Star Trek: TNG as a kid I was brainwashed by Captain Picard and his Earl Grey obsession. This is the first time I have had Earl Grey infused chocolate. The tea flavour was subtle and complemented the blueberries.

Beautiful Chocolate: Maple-glazed Walnuts & Sun-dried Lime

####Maple-glazed Walnuts & Sun-dried Lime (Vegan)#### My second favourite bar. I love nuts in chocolate. The maple-glazed walnuts make this bar crunchy, giving it some texture. The nuts overpower the lime at first, but after a few moments it shows up. It is easy to miss the lime though.

Beautiful Chocolate: Milk Chocolate Bar

####Milk Chocolate#### They ran out of the smaller bars so we had to buy the larger size. I much prefer milk chocolate over dark/semi-dark chocolate. Even though this milk chocolate is very good, I still prefer the salted caramel with the darker chocolate.

Beautiful Chocolate Bars by Anna Tolazzi

Anna Tolazzi Chocolates: Highly Recommended

The CIA and Jeff Bezos Bet on Quantum Computing

A 30 million dollar bet. That's a lot of money for D-Wave.

It's an attitude that seems to have played well with investors, but it still rankles academics. "At an engineering level they've put together a setup that's impressive in various ways," says Scott Aaronson, an MIT professor who studies the limits of quantum computation. "But in terms of the evidence that they're solving problems using quantum mechanics faster than you could classically, I don't think it's there yet." A fierce critic of D-Wave in the years following its 2007 demo, Aaronson softened his stance last year after the company's Nature paper showing quantum effects. "In the past there was an enormous gap between the marketing claims and where the science was and that's come down, but there's still a gap," says Aaronson, who visited the company's labs in February. "The burden of proof is on them and they haven't met the burden yet."

Aaronson's biggest gripe is that the design of D-Wave's system could plausibly solve problems without quantum effects, in which case it would simply be a very weird conventional computer. He and other critics say the company must still prove two things: that its qubits really can enter superpositions and become entangled, and that the chip delivers a significant "quantum speed-up" compared to a classical computer working on the same problem. So far the company has presented proof of neither in a peer-reviewed forum.

If I had to wager today, my money would be on IBM.

How to Redirect all Wordpress links to a new domain name

Today I changed the name of my website from to I did not want to set up a new installation of Wordpress and import all of my old posts, rather I just wanted to change the name of my site. The problem is that I needed a way to have all of my old pages to redirect to the page. For example, should automatically send a visitor to I also wanted to make sure that search engines, like Google, knew that was no longer active and their results should be transferred to the equivalent page.

Changing the name of a Wordpress site

On your web host Make sure that the new domain name is linked to the directory containing your Wordpress site. In my case, both and pointed to the same directory. Using either your old or new domain name it should be possible to reach your site.

Redirecting links from the old domain to the new domain

To redirect all of you old links to the new site you must modify the .htaccess file in the root directory of your Wordpress install. If your web host has enabled "mod rewrite" capabilities, then all you need to do is add the following code before the Wordpress section of the file:

# Redirect the site 
RewriteEngine On 
# Take care of 
RewriteCond %{HTTP_HOST} ^$ [NC] 
RewriteRule ^(.*)$$1 [L,R=301]

# Takes care of 
RewriteCond %{HTTP_HOST} ^$ [NC] 
RewriteRule ^(.*)$$1 [L,R=301]

# Below is the standard code Wordpress uses 
# BEGIN WordPress 
<IfModule mod_rewrite.c> 
RewriteEngine On 
RewriteBase / 
RewriteRule ^index\.php$ - [L] 
RewriteCond %{REQUEST_FILENAME} !-f 
RewriteCond %{REQUEST_FILENAME} !-d 
RewriteRule . /index.php [L] 
# END WordPress 

Change and to your old domain name, and to your new domain name. The first line of the code:

RewriteEngine On

enables the URL rewrite module that we need. The next line:

RewriteCond %{HTTP_HOST} ^$ [NC]

says that if anyone requests a page from then perform the rule on the next line. This rule is:

RewriteRule ^(.*)$$1

and it redirects the page to the equivalent page on The (.\*) means any text in the URL after, and the $1 at the end of is a variable that tells the web server to place the text from (.\*) after it. Now any website that calls a link like will now redirect to


The [L,R=301] at the end of the rule is a 301 redirect that tells any search engine or bookmark software that this is the new, permanent, home of the link and that they should update their records accordingly.

The next few lines are nearly the same and redirect all calls from to

Changing your site information in Wordpress

Once I verified that the redirects were working, I logged into my Wordpress admin panel and went to "Settings->General" where I entered in the new Site Name, Wordpress URL, and Site URL. Make sure you change change both the Wordpress URL and Site URL before saving. If you don't, this can cause an error. If things mess up, you can follow these instructions to fix things if you have FTP access to your site.

Alerting Google

I logged into Google Webmaster tools and Google Analytics and changed the name of my site from to All of my analytics and information smoothly transitioned over.

Following these steps it was relatively painless to rename my site without losing any of my old posts or creating duplicate content.

The Dancing Physicist Launches

Nearly two years ago I launched Quantum Pie as a personal blog and web site. I knew I wanted to talk about physics, dance, and other things that interested me, but the name Quantum Pie never felt completely right. Last week I performed a dance routine, to explain quantum entanglement, as part of the Institute for Quantum Computing's new building opening. After the show it hit me; I am a dancing physicist and my website should be called "The Dancing Physicist." It fits and captures who I am beautifully. So as of today is now All of the old post have been migrated over and Google has been notified of the change. I think this will also provide focus to the site. Expect even more dance and physics content.

Keep on dancing/calculating.

A faster horse

A faster horse

Great series of posters by Michael Mulvey riffing on Henry Ford's quote:

"If I had asked my customers what they wanted they would have said a faster horse."

I hope this project gets funded---these would make great office decorations.

A faster candle by Michael Mulvey

Quantum Dr. Manhattan

Physics Today has a review of the new "Before Watchmen" on Dr. Manhattan. "Watchmen" is the only graphic novel I have ever read. I am interested to see how they tackle quantum mechanics in this new series.

Silicon Qubits

Well done video providing an overview of the research. Here is the original paper in Nature. For a more general explanation of the research, here is an article from The Register. See also the University of New South Wales's press release. Why is it that University press offices are loath to link to the original paper?

Quantum cryptography: yesterday, today, and tomorrow

Chris Lee's impressive overview of quantum cryptography. Arstechnica, to my mind, does the best science reporting on quantum mechanics.

A real world example of the future of secure computation is found in the Danish sugar beet industry. All the sugar beets in Denmark are purchased by a single company. The farmers buy the rights to sell a certain volume of sugar beets to the monopolist. However, individual farmers must buy these rights based on estimates of their own production. As a result they often find themselves in the market to buy or sell rights.

Now, the last thing they want to do is buy and sell these rights through auctions run by the monopolist—monopoly power must be limited after all—because the monopolist would have the production records of every farmer and be able to use that to bid the price of the rights down. The market is setup by sellers simply listing the number of units they are willing to sell at each price. Buyers make a similar list of how many units they are willing buy at each price. The results are put together into two graphs of price and volume. Business is conducted at the intersection of these two curves.

Key to the success of this market is that no one knows who is in the market, or how much any particular farmer wants to buy or sell. A more open auction would reveal too much information, leaving farmers vulnerable to market manipulation by the monopolist and each other. So, secure computation could enable a way to create markets that are less open to manipulation, creating a fair economic mechanism.