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Is optical quantum computation easier than we thought?

In my most recent paper (read it here), Tim Ralph and I demonstrate that a single-purpose optical quantum computer might be constructed much more easily than previously thought. In fact, building such a quantum computer is within reach of present-day technology. The paper extends recent results by Scott Aaronson & Alex Arkhipov, where they showed that a type of optical quantum computer, called a ‘BosonSampling’ computer, which is classically hard to simulate, can be constructed much more easily than ‘universal’ quantum computers (i.e. the most general type of quantum computer). Such a computer is ‘easier’ to build in the sense that no active switching, feedforward or memory is required – just single photon sources, passive linear optics and photo-detection (things that we can readily do in the lab).

In our work we demonstrate that even with very substantial loss rates (whether it be source inefficiency, loss within the circuit, or detector inefficiency), such a computer can likely perform calculations beyond the reach of any classical computer. This is great news for experimentalists, for whom photon loss is a killer in their experiments. Our results show that with enough single photon sources, even with a loss rate of 50% our optical quantum computer can likely do things that classical computers can’t. This is unlike fault-tolerance results for universal quantum computers, whereby loss rates of even 0.1% are a killer. This all sounds very optimistic, but there is one drawback – no one knows what to do with this particular type of quantum computer. Aaronson & Arkhipov show that such a device almost certainly can do things that a classical computer can’t, but no actual applications have been identified. So there’s a catch – building such a quantum computer, which can outperform all the classical computers in the world put together, is within reach of present-day technology, but, no one has any idea what to do with it.

I hope these results will stimulate further research into Aaronson & Arkhipov-type devices, which will hopefully come up with some useful applications – a killer application for BosonSampling would represent a major step forward for the field. In the meantime, I hope some of the experimental groups in the optical quantum computation community will think about elementary demonstrations of such systems. Simple extensions of present-day multi-photon quantum walk experiments (e.g. this work by Peruzzo et al., and this work by Owens et al.) could act as an elementary test-bed for such systems.

The region overlapped by red and blue is where we suggest a BosonSampling quantum computer is performing a classically intractable computation - plotted against the number of photon sources and the net single photon source/detection efficiency.

Unions – Vandals & Extortionists

The recent debacle with Qantas has rekindled my thoughts about the union movement in general. I firmly believe that unions are, in general, a negative influence on our society and many of their activities amount to blackmail and economic vandalism. While there are some legitimate roles for unions, such as providing advice to members and legal representation when the need arises, the bulk of contemporary union activity centres around industrial action, or, as I like to call it, extortion.

When someone gets a job at a business, they agree to do a certain amount of work for a certain amount of pay. It is not an agreement entered into solely on one side. It is not an agreement forced onto one side by the other. It is a voluntary, mutual agreement. I find it outrageous that, after entering an agreement voluntarily, that one side (in this case the unions) retrospectively decide that actually, on second thought, they want more than they agreed to. Then, to achieve that aim, they engage in strike action, with the aim of blackmailing the business by threatening them with bankruptcy if they don’t acquiesce. This is extortion.

Imagine that you hired someone to help clean your house, and you agreed to pay them $10 an hour to help you out. Then, a few weeks later they turn up outside your house with a bunch of mates, threatening signs and refusing to work unless you agree to $20 an hour. Would you (a) give them $20 an hour, or (b) fire them an hire someone else who is willing to do the work they agreed to do? This example precisely reflects what’s happening in the union movement around the world.

You might say, why not give them $20 an hour – they’d be better off, it’s only fair? The answer is, simply, that it drives unemployment. Why employ one person for $20 an hour when you can employ two for $10? Thus, the activities of unions effectively act as a driving force for unemployment.

Those in support of unions frequently claim that unions are there to represent workers. This couldn’t be further from the truth. Unions do not represent workers, they represent paying members. Therefore, those who are not represented by the unions, and I’m specifically referring to the unemployed, get no representation whatsoever and lose out. I’d rather have solidarity with someone who is unemployed and priced out of a job, than someone with a job and a comfy lifestyle, who simply wants more.

Indeed, it is questionable whether union activity even benefits the members. When people earn more money without a corresponding increase in productivity, people have more money with which to buy goods, but the amount of goods hasn’t changed. This is inflation. When inflation occurs the RBA responds by increasing interest rates, which means that everyone is paying more on their mortgage, more on their car loan, more on their credit card, and no one is better off.

Some hardline critics of unions advocate banning unions as a solution to the problem. This solution involves taking away people’s freedom of association. So, how do we prevents these kinds of activities without taking away freedom? By giving more. Specifically, employers should be allowed to discriminate against employees on the basis of union membership. They should have the right to say “we’ll employ you, provided that you don’t join the union and engage in strike action”, and negotiate these terms into the employment contract. Secondly, because industrial action amounts to extortion, employers should be free to fire employees engaging in that kind of action and litigate for losses. This solution addresses the problem, without depriving anyone of inalienable rights.

I hope the outcome with Qantas strengthens the public’s skepticism of the union movement and opens people’s eyes to the true nature of collective action. It’s time society recognised the true face of unions. They are not there to help people out or make sound economic decisions. They are there to accumulate power into the hands of union bosses and thugs so they can later run for public office and become a minister (or undemocratically overthrow a Prime Minister). This needs to stop.

New paper: Optimising number resolving photo-detectors using classical post-processing

Many present day quantum optics experiments, particularly in optical quantum information processing, rely on number-resolving photo-detection as a basic building block. In this paper we demonstrate that a simple classical optimisation technique can sometimes be employed to post-process the detector signature and improve the confidence of the measurement outcome in the presence of photon-number errors such as loss or dark-counts. While the regime in which this technique is applicable is rather restrictive, and will likely not be very useful for the large-scale quantum information processing applications of the future, the ideas presented might be employed in some present-day experiments where photo-detectors are typically very poor.

Read full paper here.

New DJ Rohde mini-album

DJ Rohde is pleased to announce the release of his latest mini-album, Die for Belief.

Listen to and download Die for Belief here on Jamendo.

In defence of Israel

Every country is deserved of criticism. I’ve yet to find a country whose domestic and foreign policies I agree with in their entirety. As such, it is entirely justified to level criticism when criticism is due. What I object to however is criticism that is mounted in a highly discriminatory and ad-hoc manner. I have Israel in mind.

There are most certainly Israeli government policies of which I am critical. I criticise the Israeli government for not being as pro-active as it could be in regard to finding a solution for peace with the Palestinians. What I object to however is exaggerated and discriminatory criticism. I find, ever increasingly, particularly amongst the so-called ‘intellectual elite’ in Australian society (i.e. academics with an overinflated sense of self-importance, who consider themselves the pinnacle of mankind’s intellectual achievement) that criticism of Israel is disproportionate and rife, hypocritical and downright discriminatory. Sure, I don’t agree with everything that Benjamin Netanyahu says or does, but does this really justify a widespread, concerted international effort to criticise, demonise and undermine Israel? Aren’t there other countries more deserving of criticism than Israel? Why is there an all-out effort to attack Israel, on the basis of territorial disputes and counter-terrorism efforts, when there are so many other wrongs in the world? Why do we have organisations like this one, why are there proposed labour union-sponsored academic boycotts in the UK, and why is our own Australian electorate of Marrickville proposing a total boycott of all Israeli products, when there are so many others more worthy of criticism? The answer is, very plainly, that it’s discrimination and racism. People hate Israel. There, I said it – people hate Israel. Do the same organisations, unions and local councils suggest that we boycott China for oppressing Tibetans? No. Do they boycott Australia, the UK and the US for the wars against Iraq and Afghanistan (which I know they disagree with)? No. Do they boycott Iran for persecuting the minority Bahai faith, or Saudi Arabia for executing homosexuals and stoning so-called ‘adulterers’ (i.e. rape victims)? No. When criticism is due, give it, but keep it in proportion and keep it fair. The international movement against Israel is not founded on fact and objectivity – it is founded on hatred and discrimination. I don’t agree with everything Israel says and does, but the same applies to every other country on Earth. Singling out a single country, and repeatedly attacking them for policies we disagree with, while ignoring the huge injustices in so many other countries is discrimination, plain and simple.

In a region of the Earth ruled by tyrants, dictators and Islamist fundamentalists, Israel is the only modern, Western-style, progressive, parliamentary democracy. Israel is a multicultural society, with a huge Muslim minority (about 20%) , and even takes a world-leading social stance by recognising same-sex marriage. Do they get credit for this? No. Instead her critics choose to focus all their efforts on degrading her and insinuating that she is a racist apartheid country, while ignoring her strengths, and completely forgetting the injustices in so many other countries including their own.

If Israel is deserved of a boycott for her attempts to protect herself against terrorism, then so is Australia for its participation in the Iraq and Afghanistan wars. If Israel is criticised as an ‘apartheid country’, then we should look at our own – Israel has far larger ethnic minority groups than Australia does, all of whom have full democratic rights.

Israel is more like our own country than any other in that region of the World. Yet, there is an enormous international movement, led by the radical left and the ‘intellectual elite’, to demonise that country. Before you make a concerted effort to alienate Israel, take a long, hard look at your own country.

If you gave me a choice to live in any country in the Middle Eastern region, I know where I’d prefer to live, without a shadow of a doubt – and it wouldn’t be the country where they amputate my hands for opposing the rulers or stone to death my wife for being raped.

Rejected!

I recently submitted my first paper to the Journal of Universal Rejection. Here’s my correspondence.

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Dear Editor,

Please find attached our manuscript “Entanglement dynamics and quasi-periodicity in discrete quantum walks” for consideration for rejection from The Journal of Universal Rejection. In this paper we study the use of the quantum walk formalism in the preparation of entangled states as a resource for other quantum information processing tasks. We show that, surprisingly, highly irregular, almost chaos-like dynamics emerge when boundary conditions are imposed on the graph on which the walk is taking place. As numerous experimental groups are beginning to experimentally demonstrate elementary quantum walks, our study is topical and relevant. We hope you will consider our paper for rejection.

Sincerely,

Dr. Peter P. Rohde
BE (Hons I), PhD

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Dear Dr. Rohde,

Thank you for your submission “Entanglement dynamics and quasi-periodicity in discrete quantum walks” to the Journal of Universal Rejection.

A thorough review of your paper led us to the conclusion: revise and resubmit.  Here is what we would like to see:
* Perform a linear walk experiment on an infinite graph
* Put in a picture of the Bifurcation diagram of the logistic map, because that is cool, and
* Translate your paper into rhymed couplets.

Let me know if you should need further clarification about any of these suggestions.

Should you carry out the above steps, acceptance is not guaranteed. We will of course need to review your paper again.

Best regards,
Caleb

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Dear Dr. Emmons,

Thank you for taking the time to review our manuscript. Regrettably our institution is undergoing funding cuts which will rule out the possibility of performing an experiment with an infinite sized graph. Thus we will be unable to satisfy the requirements of the reviewers.

Kind regards,

Peter Rohde.

Marijuana law reform

An issue which I feel very strongly about, but which for some reason I’ve never blogged about before is the legalisation of marijuana. While I don’t advocate marijuana use, in my mind there is no moral justification for the criminalisation of marijuana for numerous reasons:

1. Marijuana has been systematically shown to be less physically harmful and less addictive than both alcohol and tobacco, both of which are legal. The following plot comes from Wikipedia (see article for reference), which shows affinity for dependence and the physical harm of many common drugs. Notice that marijuana is less harmful than both alcohol and tobacco on both axes.

2. If people want to harm themselves, this is a personal choice and individuals need to decide for themselves whether they are willing to accept the risks. This is exactly our policy on alcohol and tobacco, so why not for marijuana? Tobacco, which is consistently rated as more harmful than marijuana, including numerous fatal illnesses, is tolerated on exactly this basis – it’s a personal choice and people need to make the decision for themselves.

3. Marijuana use does not cause violent crime and anti-social behaviour in the way that alcohol, heroin and crystal meth do and therefore there is no moral justification for treating marijuana users in the same way as violent criminals by throwing them into jail.

4. The effects of jail are far more heinous than marijuana use. When you throw someone into jail you destroy their lives – their career, financially, their family, and you leave them with a criminal record, ensuring that they will never have a decent job again. This is far worse than the effects of even heavy marijuana use.

5. It’s totalitarian for a government to trot into people’s living rooms and tell them what they can and can’t do in the privacy of their own homes. This is on par with the anti-sodomy laws of countries like Singapore.

6. Studies have consistently found that legalisation of marijuana does not result in a noticeable increase in marijuana use. Most notably, a recent study in Portugal found that decriminalisation of marijuana did not lead to an increase in marijuana use. Additionally, Holland, which has the most liberal marijuana laws in the world, has lower teen marijuana usage rates than Australia, the UK and the US, all of which have relatively tough marijuana laws.

7. In recorded medical history there has never been a single recorded case of marijuana overdose. Experts believe that to overdose on marijuana would require smoking several kilograms of marijuana, which is impossible. Furthermore, marijuana does not cause physical dependence – heavy alcohol use does.

8. Marijuana has many proven medical applications, including in the treatment of eating disorders, depression, mania, bipolar disorder, anxiety and panic disorders, loss of appetite associated with chemotherapy or HIV medication, and pain relief. Before the invention of aspirin (which causes thousands of deaths worldwide each year) in the 19th century, marijuana was a popular and effective form of pain relief.

9. Education, rather than criminalisation, is the correct approach to discouraging marijuana use. This is what we do with alcohol and tobacco – every cigarette packet contains a health warning, and there are countless media ads highlighting the dangers of alcohol and tobacco use. In the last decades the percentage of Australians who smoke has been drastically reduced. It’s not because of criminalisation, but because of our investment into educational and awareness campaigns.

10. Legalisation of marijuana could potentially contribute billions of dollars to the budget if it were taxed in the way that alcohol and tobacco are. If this money were invested into education, rehabilitation and health, the benefits would be enormous.

11. By removing marijuana from the black market and bringing it above ground, organised crime groups would lose a major source of their revenue, reducing criminal activity.

12. We have spent billions of dollars wasting law enforcement and judicial effort on enforcing petty cannabis laws. Instead of wasting billions of dollars, why not gain billions in tax revenue.

In summary, I believe that criminalisation of marijuana is excessive, counterproductive and downright immoral. It is wrong to treat people as criminals for doing something in the privacy of their own homes which hurts no one other than themselves – marijuana use is a victimless crime. The Australian government should immediately reconsider its approach to marijuana in light of well established scientific and medical facts. The social, economic and individual benefits would be substantial.

New paper: Entanglement dynamics and quasi-periodicity in discrete quantum walks

We study the entanglement dynamics of discrete time quantum walks acting on bounded finite sized graphs. We demonstrate that, depending on system parameters, the dynamics may be monotonic, oscillatory but highly regular, or quasi-periodic. While the dynamics of the system are not chaotic since the system comprises linear evolution, the dynamics often exhibit some features similar to chaos such as high sensitivity to the system’s parameters, irregularity and infinite periodicity. Our observations are of interest for entanglement generation, which is one primary use for the quantum walk formalism. Furthermore, we show that the systems we model can easily be mapped to optical beamsplitter networks, rendering experimental observation of quasi-periodic dynamics within reach.

Read full paper here.

Public transport?

I never figured out why so many of my economically conservative friends are opposed to investing in public transport. After all, we subsidise private transport in the form of roads, bridges, highways and public parking. Public transport takes load off this infrastructure, which means we need to invest less into it. This could make heavy investment into public transport revenue positive. Why upgrade a city road to half a dozen lanes to reduce congestion, when the allocation of a single bus lane is cheaper? Some question the compatibility of this view with my generally pro-market, Libertarian-leaning views. However, these views are completely consistent. Libertarians believe in reducing tax-payer burden and public transport is one of the few areas where tax-payer spending can reduce the overall tax burden.