One of the groundbreaking achievements of mankind in the past century is certainly the invention of computer and the advances in the field of information processing. It enabled any kind of data to be stored, manipulated and shared in many ways allowing for a boost in technology as well as in fundamental science. Even though being virtually absent in our daily lives two decades ago, today information processing is an integral part of human civilization, a fact that also underlines the significance of the advances in this field in recent years. Thus, in fundamental research, exploring novel means to improve the performance of computers is a very active topic and will likely to remain such in the foreseeable future.

A significant leap forward in information processing is being able to use quantum mechanical laws for data storage and calculation, the laws which are valid for microscopic objects and very low temperatures but unfortunately not for the world we perceive - the ambient conditions. Yet, there has been increasing laboratory efforts to exploit quantum superposition in data processing, a principle in quantum mechanics allowing for faster and resource-efficient storage and processing superior to the classical computers we have today, and scientists are continuously taking steps to realize a quantum computer which could be made use of outside laboratories.

A critical drawback of these potential quantum processors, however, is their sensitivity to operating conditions which can not be controlled perfectly even by state of the art experimental techniques. Although there are various approaches to realize a quantum computer using different materials and different architectures, each of them suffers from this drawback: one can do computation or store data only for a very short time before everything gets destroyed by coupling to the environment. A theoretical proposal aiming to eliminate this challenge focuses on using the topological phase of a physical system which is tolerant to the changes/imperfections in operating conditions causing the faults. The topological phase can be envisaged as a rubber ball having no holes in its shape: even though one can deform it, say by kicking or squeezing it, it will stay as a ball and will not be, say a doughnut having one hole in its shape. In this case, a doughnut and a ball are in different topological phases. Accordingly, by using the topology of a physical system to compute and to store data, one can implement fault-tolerant quantum information processing.

We use nanowires, tiny conductive wires thousand times thinner than a hair, and bring them in contact with a superconductor to realize a unique topological phase of matter so as to prove it useful as a building block for topological (fault-tolerant) quantum information processing. Using the right materials and fine-tuning the electric and magnetic fields, we find the sweet spot exhibiting the topological protection. This topologically protected phase supports the so-called Majorana fermions (exotic particles somewhat similar to the electrons in a solid) in a nanowire-superconductor hybrid system. We try to measure and manipulate these Majorana fermions since controlled manipulation of Majorana fermions could pave the way for quantum computers sprawling out of the laboratories, replacing the computers we use today.

On graphene, buckyballs and CNTs

Why graphene is interesting from a physicist's point of view:

(i) In graphene the electrons contributing to an electrical current behave as they do not have a mass. This is special to graphene and some other novel materials. (First discovered in graphene)

(ii) The conductance of graphene, although a semi-metal, can be tuned using the field effect. This is how usual transistors work. Why are there no metallic transistors? Because we can not tune the conductivity by electrical means (so simple). This remarkable property of graphene arise from its two-dimensional nature. It is so thin that electric field is not screened by conduction electrons. Because of this, graphene is expected to play a dominant role in thin-film transistors, the transistors that are so thin that they are transparent and could be used on screens. Also, graphene-based devices can be flexible and so will probably be utilized in wide range of applications.

(iii) In graphene, the electrons contributing to a current are not scattered during flowing from one point to another as much as in other materials. That is, the mobility of the electrons are very high. (conductivity = mobility x electron concentration) This is because the scattering (what causes resistance as we know it) is suppressed owing to the chirality of the conduction electrons of graphene: they have to change their pseudo-spin to scatter away from their trajectories. And electrons do not like that.

What brought graphene a Nobel Prize in phyiscs is that after the first study on graphene, all the laboratories started to investigate this material. This is mostly because:

(i) It is so easy to fabricate graphene-based devices as pointed out in this thread by other people as well. You can obtain a graphene using the so-called mechanical exfoliation method. Why they came up with such a cool-sounding complicated name is no one was fond of saying "oh, we got it using a scotch tape."

(ii) From an engineering (practical) point of view, graphene is really promising in electronic applications. So the funding was quite well.

The physicists K. Novoselov and A. Geim were awarded for their first paper about graphene: "Electric Field Effect in Atomically Thin Carbon Films" (http://www.sciencemag.org/content/306/5696/666.short) Check how many citations this article has. It has been less than a decade.

Related carbon-based nano-materials:

Buckyballs are molecular spheres made of 60 carbon atoms. Due to their nature, they are not particularly useful for transport measurements (where you apply a voltage and measure the current flowing), because it is not easy to fabricate contacts on a tiny sphere. (I have experience only in transport measurements so I don't know much about them.) But a little more than a decade ago, they were utilized in matter-wave interference measurements. Remember the particle-wave duality? For example, electrons are particles but they can also interfere as if they also have a wave-like nature. The experiments on electrons demonstrating the electron-wave interference have been performed in early 20th century. From the pioneering work of French physicist De Broglie, we now know that there is a particle-wave duality. And buckyballs showed also a wave-like nature! They made two beams out of buckyballs, they made the beams collide and obtained an interference pattern. This experiment was performed in 1999: "Wave–particle duality of C60 molecules" (http://www.nature.com/nature/journal/v401/n6754/abs/401680a0.html) Currently, people are trying to do similar experiments on viruses; even larger particles. Maybe in the future we will obtain an interference pattern also out of living things such as bacteria or so. Or maybe cats! Who knows?

Carbon nanotubes (CNTs) are just rolled up graphene. Also from a quantum mechanical point of view, they are treated as such: To obtain the electronic properties of carbon nanotubes, we start from a graphene sheet. Then we roll it up. This is equivalent to the Bloch problem, the problem how we now calculate the energy bands of crystals. Of course, you can roll a graphene in many ways. This can result in CNTs with different diameters and with different orientation of carbon bonds along the tube axis (called helicity). The diameter and the helicity of CNTs determine their properties. This way CNTs can be metallic or semiconducting. (Note that graphene is a semi-metal.) CNTs are very promising for a large range of applications. First, they are really really thin, even though they are mechanically extremely robust. This we all have probably already heard of. They also share some similarities with graphene. So for example scattering in CNTs are also suppressed because of the pseudo-spin of the conduction electrons. This pseudo-spin is locked to the movement direction of the electrons, so they can not change their direction of propagation without changing their pseudo-spin. That is, the scattering is suppressed. However, the future of CNTs in electronic applications might be in danger. This is because even though there has been quite some time since the discovery of CNTs, we still can not control the diameter and the helicity of CNTs: We can not produce arbitrary amounts of identical CNTs. And this is of course a big big challenge for industry. Because of this, their popularity in transport measurements are decreasing. Not so many labs are investigating CNTs as they did 10 years ago.

ultimate abstract

Humanrace needs energy in order to survive (1-4). Recent developments proved to be useful in terms of exploring alternative approaches (2, 5) to circumvent the energy problem (EP), and in utilizing novel techniques for the benefit of mankind (6-10). However, so far, no study could achieve 100% sustainability while maintaining the feasibility in industrial as well as in domestic use (8, 11-17). Here we approach the EP by studying BN-Graphene-Topological Insulator heterostructure transport devices. Our devices unambiguously reveal a quantum transport mechanism that, in terms of energy conversion, can reach up to 99.6% sustainability values, with the energy gain technique we demonstrate being readily applicable to human life. Our unprecedented results can, in principle, solve the EP.

I'm sorry

That you are now far away
That I wasn't with you
When you wanted
When you needed.
Little did I know
I was stupid
Those you understood
And did not expect much
No one did.
I am not to blame I know
Some say 'forgive yourself'
'Time will pass'
'And it will all be over' they say
But why would I forget you
For everything I owe you?
I want you to stay with me
A little longer
So I can feel sorry
This I want to do forever

Disclaimer for future me: This is not about a break up

A change

A change is good for everybody. We feel happy when we have an influence on our lives and make decisions. But some people like to be safe. Some people do not want to risk much. They can not make radical changes. Maybe I am also one of those.

I thinking of going to bed for a change. Yeah, it already felt good.

i need answers

Having nearly infinite pathways to pursue in life, how do we decide on what we want to do in the future? Let alone future, isn't it already hard enough to find out what we want now? So what do we (have to) consider to make our choices which are going to form our future, say, ten years from now? To what extent should the physical and mental abilities play a role? Is our future defined by what we are able to or what we want to?(*) Is it even foreseeable at all whether these choices will turn out to be reasonable? Or does it just sound comforting that we can make rational choices about our future even though we have no idea what the future will bring in years? Because otherwise, we have to admit that the choices we make now are actually not the best and the most suitable ones for our future; that would also mean we are actually incapable of having the full control of our lives.

(*) Can there be a difference between what we want and what we can? 1. If so, what kind of an impact would that have on a self-decision process regarding one's future? 2. If so but there should not be, should we put the blame on them for not knowing enough about themselves and for chasing rainbows? 3. And if not, why? Is it rather unlikely that one can live fully satisfied, if they are not pursuing the path, which happens to be the most suitable one (in the sense that it is limited by physical and mental abilities the least), from all the possible ones? Should we feel successful at what we do all the time? This would also raise the question: how much importance should we have to put on our egos?

Es secimi üzerine oylesine bir yazi

hepimizin bildiği bir temel fıkrasında dursun temel'e sorar: "temel, söyle bakalım hatunun ne türlüsü iyidir, güzeli mi aptalı mı?" temel "aptalı" diye cevap verir. şaşıran dursun hayretler içerisinde temel'e seçiminin nedenini sorar. cevap malumunuzdur: "güzellik geçicidir." bu konuya değinen ilk ve tek söylem olmadığı açık bu fıkranın. o zaman bu popüler konuyu biraz deşelim, bakalım altından neler çıkacak.

tarih boyunca canlıların birincil amacı, türlerinin nesillerinini koruyabilmek, sonraya taşıyabilmek olmuştur. bu savı insanlar için de kabul edebiliriz. çoğu zaman doğada dişinin sağlıklısı (doğada güzellik sağlıktır), erkeğin de güçlüsü kazanmıştır hemcinsleriyle girdiği savaşı. bunun örneğini çok yerde görebiliriz. doğada güçlü olan, sağlıklı olan neslini devam ettirir hiç şüphe yok ki. gelelim insanoğluna. insanoğlu temelde gelişmiş bir memeli ve insanlık için de benzer durum geçerli. ancak ufak görünen ama aslında bütün denklemleri baştan yazdıran bir farkla: insanoğlunun yaşayışında sosyallik çok önemli bir rol oynar.

tarım kültürünün gelişmesiyle binlerce yıl önce, yerleşik hayata geçilir. bu ise sosyal yaşama zorunluluğunu beraberinde getirir. artık insanoğlu tek başına değildir, bir yere, bir toprağa aittir, başka bireylerle birliktelik kurmaya başlar. yazı bulunur, yasalar konur, ticaret ağları ortaya çıkar, tıp ortaya çıkar. bin yıllar sonra ise sonuç malumunuzdur: şu an dünyada hüküm süren sosyal toplum düzenleri. bu durum ise bizlerin hayatını bir çok açıdan değiştirir. konumuzla ilgili olarak; eş seçiminde, neslimizi devam ettirme kaygımızda önemsediğimiz kriterler, doğada benzeri (bildiğimiz kadarıyla) bulunmayacağı bir biçimde başkalaşır. insanoğlu eşini seçerken doğadaki formülü birebir kopyalamaz: erkeğin güçlü ve sağlıklı olması, en önemli kriter değildir! kimine göre karakter, kimine göre ekonomik durum, kimine göre otorite, kimine göre zeka. ancak kimse kas gücünden veya kaç sene daha yaşayacağından bahsetmez. neden çok açık. insanoğlunun neslini devam ettirebilmesi için güçlü olması gerekmez. sosyal toplum düzeni, üyelerinin birbiri arasındaki ilişkilerine büyük önem verir. bu düzende ise, ilişkileri kas gücü veya yaşımız yönetmez. yukarda saydığımız birçok etmen birlikte etkiler.

peki neden kadınlar sosyal düzene uyum sağlayıp eş tercihlerini değişen dünya gerçeklerine göre yaparken, erkekler hala doğadan aldığı formülü çok da değiştirmeden uygular? erkekler için birinci tercih güzelliktir. bunun istisnaları şüphesiz ki vardır ama kimse, en genel kriterin güzellik olduğunu yadsıyamaz. kadınların nesillerini devam ettirmeyi, erkeklerden daha çok önemsemesine bağlıyorum bunu. bir anne için çocuğunun sağlığı belki de o en önemli şeydir. babalar alınmasın kesinlikle, onlar için de çok önemlidir çocuklarının sağlığı. ama bir erkek eş seçiminde "çocuğumu nasıl büyütür" sorusunu bir kadın kadar sormaz eşine.

modern düzen kadınların eş seçimlerini kökten etkilemişken, erkeklerin modernleşme yarışında geri kaldığı kanaatindeyim. hepimizin farkında olduğu üzere, sosyal düzende doğa kanunları işlemiyor. bunu erkekler er ya da geç fark etmeli.

bir teori daha var ki göz ardı edemeyiz. belki de insanoğlu için en önemli şey türünü devam ettirmek değildir doğadaki benzerlerinde olduğu gibi. belki de böyle açıklayabiliyoruz çocuk doğurmak ya da evlenmek istemeyen bireyleri. belki eşcinselliğin varlığı da bununla ilgili. belki de erkek bu yüzden eş seçiminde "çocuğum nasıl büyür" faktörünü güzelliğin arkasına itebiliyor. peki ne o zaman en önemli şey? ego mu? eğer öyleyse burada büyük bir ironi gizli. insanlar bir yandan zamanla sosyalleşirken, birbirleriyle iletişim yoğunluğu tam gaz artarken; aynı zamanda tür bilincini yavaş yavaş yitirmekte, türünü devam ettirme fikri yaşayışında gitgide önemsizleşen bir rol oynamakta, bireysellik ve ego ön plana çıkmakta.

yazdığım çoğu şey öznel olabilir ancak su götürmez bir gerçek var: doğadaki benzerlerimiz yemek derdindeyken biz politik tartışmalara girebiliyoruz. dünyada artık sadece doğa kanunları işlemiyor insanoglu için. 


24.05.2011