A quantum computer is device for computation that uses the phenomena of quantum mechanics to perform operations on data. Because of the quantum mechanical phenomena, such as entanglement and superposition of states, quantum computers have great offers in the field of computations and data handling. The distinctive feature of a quantum computer lies on its ability to store and process superposition of numbers.  This potential for parallel computing points out that some problems can be efficiently solved using quantum computers compared to the classical one. Shor’s algorithm, for example, which solves the problem that ‘Given an integer N, find its prime factors’, shows that quantum computer should be able to efficiently factor large numbers. The field appears to be of great interest since most data encryption schemes (in cryptography-science of information security) relies on the inability of the classical computers to factor large numbers.

To have an experimental realization of a quantum computer, there is a requirement of an isolated quantum system which will act as qubits and the presence of controlled unitary interactions between the qubits that allow construction of a controlled-NOT (CN) quantum logic gate. Quantum logic gates are building blocks of quantum circuits which operate on small numbers of quantum bits (qubits).  Quantum logic gates, unlike the classical logic gates, are reversible.  A CN quantum logic gate is one of the commonly used logic gates which operate on two qubits (we label the qubits as and ).   The CN gate transforms the state of the two qubits from to where is an addition modulo 2. The CN gate represents a computation at the most fundamental level, that is, a certain ‘target’ qubit is flipped depending on the state of a ‘control’ qubit .

Christopher Monroe and his team from National Institute of Standards and Technology (NIST) Laboratory in Boulder, Colorado, who are working on ion-trapped quantum computers, have been able to demonstrate the operation of a two-bit controlled-NOT quantum logic gate operating on prepared quantum states.  In their experiment, the two qubits comprise two internal (hyperfine) states and two external (quantized motional harmonic oscillator) states of a single trapped atom using a single beryllium ion (Be⁺). The trapped ions are first laser cooled to zero-point energy for them to stay in the ground state.   In the trapped-ion architecture, the qubits are associated with the internal states of the ions and information is transferred between the qubits through a shared motional degree of freedom. With this configuration, decoherence can be small so it will be easier to extend the idea to large registers and the qubit readout will have a nearly unit efficiency.

To realize the CN gate, three sequential pulses of the Raman beams is applied to the ion, namely the π/2 pulse applied to the carrier transition, a 2π pulse applied on the blue side band transition and a π/2 pulse applied to the carrier transition with a π phase shift relative to the first pulse. The truth table for a CN gate operation is given as:

Input State            Output State

In their experiment, the key features of the CN gate was demonstrated by verifying that the populations of the register follow the truth table and by demonstrating the conditional quantum dynamics associated with the CN operation. On the results of the experiments of Monroe, et. al., decoherence were still present. The decoherence were caused by instabilities of the laser beam power, the position of the ions relative to the laser beams, the fluctuation of external magnetic fields, instabilities in the trap drive frequency and voltage amplitude, dissipation of the ion motion and some spontaneous emission caused by off-resonant transitions. The single ion quantum register in the experiment comprises only two qubit which is not useful for computations. The next step of the researchers then is to apply their operation techniques to many ions cooled at a state of collective motion for the possibility of implementing computations on larger quantum registers.

Reference:

1. C. Monroe, D.M. Meekhof, B.E. King, W.M. Itano, and D.J. Wineland, Physical Review Letters, Vol. 75, Num. 25, December 1995.

Einstein maintained that quantum mechanics entails “spooky actions at a distance” (the interaction of two objects which are separated in space with no known mediator of the interaction); experiments have now shown that what bothered Einstein is not a debatable point but the observed behavior of the real world. He called this “spooky action at a distance” because he didn’t know about decoherence, so it seemed spooky to him.

In May 1935, Albert Einstein, Boris Podolsky and Nathan Rosen published the EPR Paper, an argument that quantum mechanics fails to provide a complete description of physical reality. The theoretical and experimental work it inspired remain remarkable for the vivid illustration they provide of one of the most bizarre aspects of the world revealed to us by the quantum theory. Their work describes a situation ingeniously to force the quantum theory into asserting that properties in space-time region B are the result of an act of measurement in another region A; so far from B that there is no possibility of the measurement in A exerting an influence on region B by any known dynamical mechanism. Under these conditions, Einstein maintained that the properties in A must have existed all along. The fundamental result that they were trying to show in their paper was not that quantum mechanics is wrong. They did, in fact, acknowledge that quantum mechanics could be used to make highly accurate statistical predictions about experiments. They were interested mainly in what the fundamental properties of reality are.

Their paper involves a paradox — a thought experiment which challenged long-held ideas about the relation between the observed values of physical quantities and the values that can be accounted for by a physical theory. According to its authors the EPR experiment yields a dichotomy. Either:

1. The result of a measurement performed on one part A of a quantum system has a non-local effect on the physical reality of another distant part B, in the sense that quantum mechanics can predict outcomes of some measurements carried out at B.
2. Quantum mechanics is incomplete in the sense that some element of physical reality corresponding to B cannot be accounted for by quantum mechanics (that is, some extra variable is needed to account for it).

An enormous set of data, generated out from the apparatus used in the said experiment, by many, many runs. Thus, as Einstein partly said on his letter to Max Born: “…I am therefore inclined to believe that the description of quantum mechanics…has to be regarded as an incomplete and indirect description of reality…”

Paul Adrien Maurice Dirac was born on 8th August, 1902, at Bristol, England. He was educated at the Merchant Venturer’s Secondary School, Bristol, and then went on to Bristol University where he studied and obtained B.Sc. in Electrical Engineering degree. He also studied mathematics for two years at Bristol University, later going on to St. John’s College, Cambridge, as a research student in mathematics. He received his Ph.D. degree in 1926. He became a Fellow of St. John’s College and also held the position Lucasian Professor of Mathematics at Cambridge. Dirac was given The Nobel Prize in Physics 1933 together with Erwin Schrödinger for their discovery of new productive forms of atomic theory. He then gave a lecture regarding matter and antimatter specifically on electrons and protons on the Nobel Lecture he delivered on December 12, 1933.

In his lecture, Dirac emphasizes that the procedure he came up with is successful in the case of electrons and positrons and that he hoped that in the future some such procedure will be found for the case of the other particles. He considered the electron and positron because in their case, the theory has been developed further. He outline the method for electrons and positrons, showing how one can deduce the spin properties of the electron, and then how one can infer the existence of positrons with similar spin properties and with the possibility of being annihilated in collisions with electrons.

The general quantum mechanics at Dirac’s time describe the motion of any kind of particle, no matter what their properties are. However, it is only valid when the particles have small velocities and fail when the effect of relativity comes in. Basically, Dirac started with an equation connecting the kinetic energy and momentum and let this act on a wave function since we can view and as operators. The equation is not linear in the kinetic energy and momentum. Now, according to the general requirement of quantum mechanics, the wave equation should be linear in the operator and in order that the equation may have relativistic invariance, it must also be linear in . Thus, new variables where introduced which give rise to the spin of the electron and give rise to some rather unexpected phenomena concerning the motion of the electron. In practice, the kinetic energy of a particle is always positive however the equation allows two kinds of motion. Only one motion is familiar. The other corresponds to electrons with a very peculiar motion. The faster they move, the less energy they have, and one must put energy into them to bring them to rest called the positron which corresponds to the motion of an electron with a positive charge instead of the usual negative one. We can then look at the process of annihilation where an ordinary electron, with positive energy, drops into a hole, fill up this hole and electromagnetic radiation is liberated. On the other hand, creation of an electron and a positron from electromagnetic radiation should also be observed.

Also, he added that if we accept the view of complete symmetry between positive and negative electric charge so far as concerns the fundamental laws of Nature, we can also get negative protons. However, the process will be more rigorous since protons are more complicated and the theory would require reliable basis which was not yet discovered at that time.

This article contains a summary of Max Born’s Nobel lecture entitled, “The statistical interpretation of quantum mechanics”.

In 1926, shortly after the formulation of the Schrodinger’s equation, Max Born studied the scattering of a beam of electrons and was led to his interpretation of the wave function in the said equation.

Born’s statistical interpretation states that:
The probability of finding an electron, described by the wave function, Ψ (x,t), in the region lying between x and x+dx is given by:

where

is the complex square or Ψ*Ψ[1]

He, therefore, introduced the statistical point of view into modern physics.[2] For this invaluable contribution in the field of quantum mechanics, Born was awarded the Nobel Prize in Physics in 1954.

During his Nobel lecture, Born accounted the developments in the field of quantum mechanics that led him to his statistical interpretation. He mentioned that in 1925, he and Werner Heisenberg formulated the matrix mechanics representation of quantum mechanics. Wolfgang Pauli consequently calculated the stationary energy values of hydrogen atom by means of the matrix method and from this moment onwards, there could no longer be any doubt about the correctness of the theory.

In 1926, Louis de Broglie formulated the de Broglie hypothesis claiming that all matter, has a wave-like nature. He related wavelength (denoted by λ) and momentum (denoted by p) as:

λ=h/p

where h is the Planck’s constant

Schrodinger, following de Broglie’s wave-particle duality theory of matter, constructed his famous equation that describes how the quantum state of a physical system changes in time. This equation can be mathematically transformed into matrix mechanics.

Not long after, Born developed his statistical interpretation. Not only was it developed from Schrodinger’s equation but from Einstein’s idea as well. Einstein interpreted the square of the optical wave amplitudes as the probability density for the occurrence of photons. For Born, this concept could be carried over to the Ψ-function.  Ψ*Ψ represents the probability density for electrons.

Furthermore, Born also emphasized that the indeterministic statistical interpretation should be accepted despite the strong oppositions of some respected physicists like Erwin Schrodinger, Louis de Broglie and Albert Einstein. He believed that Heisenberg’s uncertainty principle contributed to the swift acceptance of the statistical interpretation of the Ψ-function.

Uncertainty principle states that certain pairs of physical properties cannot both be known to arbitrary precision. Its meaning, according to Heisenberg, is that it is impossible to determine simultaneously both the position and velocity of an electron or any other particle with any great degree of accuracy. With this, Born had this to say, “Can absolute prediction really be made for all the time on the basis of the classical equations of motion?”

Towards the end of his lecture, Born made these two statements: “Classical physics cannot be used as an objection to the essentially indeterministic statistical interpretation of quantum mechanics” and that “I am emphatically in favour of the retention of the particle idea.”[3]

Through his statistical interpretation, Max Born showed that the solution of the Schrodinger equation has a physical significance.

[1] Stephen Gasiorowics. Quantum Physics, 3rd ed. (John Wiley and Sons, Inc., 2003) p. 28.
[2] Walter Greiner. Quantum Mechanics: An Introduction, 4th ed. (Springer-Verlag, Berlin) p.65
[3] Max Born. The Statistical Interpretation of Quantum Mechanics. Nobel Lecture, 1954.

Computers today are now fundamental part of people’s lives. It is used in a lot of applications such as in business, communication, security systems, sciences and etc. Developing fast classical computer has come to its fundamental limitation and aiming this type of computer would rely on making the device smaller to make chips’ transistor switch faster. However, when they begin to approach 10 nanometers, electrons will start revealing their quantum nature and very strange things will happen. When transistors reach those infinitesimal dimensions and electrons start showing their true colors, this will be the start of vast new frontiers for computing which is based on quantum computers.

Finding something to act as quantum bit or qubit whose quantum state can be read and manipulated is the first thing to remember in building a quantum computer. However, quantum state is a frail thing for it can easily be changed by just a fluctuation of magnetic field or a strong-willed photon interaction. By then, two physicists from Austria’s University of Innsbruck, Juan Ignacio Cirac and Peter Zoller, theorized that a string of ions held fast in a vacuum by an electromagnetic field and cooled to within a few thousandths of a degree above absolute zero could act as stable qubits and form the basis of a quantum computer. There are also research group in NIST that had lot of experience in trapping and cooling ions from their work of atomic clock and one example of their work is trapping beryllium ion as qubit to perform logic operations which is the main key in running a quantum computer.

Even before, physicists have come up with at least half a dozen ways to do quantum computation. This includes using atomic nuclei in organic compounds as qubits and manipulating electrons within superconducting loop. However, it’s hard to handle more than a dozen of qubits which will never lead to an efficient quantum computer that requires hundreds if not thousands. It’s hard to create a full scale ion trap big enough to accommodate that many qubits. Therefore, the only way to build quantum computer is to build the equivalent of quantum integrated circuits. Trap technique is the best way to create these quantum transistors that work the same way like to shrink them down enough and put many of them of the same piece of semiconductor.

Quantum computers could one day replace silicon chips, just like the transistor once replaced the vacuum tube. But for now, the technology required to develop such a quantum computer is beyond our reach. Most research in quantum computing is still very theoretical. There is difficulty in some aspect of building this quantum computer because an equivalent of very large scale integration would require handling the control circuitry just to move the ions around. Five thousand ions would need many dozens of lasers for cooling, detection, and gate operations which should be precisely controlled in coordination with the ions’ motion in the trap. Therefore, this needs a great deal of infrastructure, including a powerful classical computer, to run a useful quantum computer. The most advanced quantum computers have not gone beyond manipulating more than 16 qubits, meaning that they are a far cry from practical application. However, the potential remains that quantum computers one day could perform, quickly and easily, calculations that are incredibly time-consuming on conventional computers. But there is still hope since scientists are running today and plan to run in the near future will almost certainly lead to insights that could make full-scale quantum computing.

Wolfgang Ernst Pauli was one of the great contributors of quantum mechanics. He was an Austrian-born Swiss physicist and a Nobel laureate. He was born in Vienna Austria – Hungary on April 25 of year 1900. In 1918, he finished his early education in Vienna. He received his Ph.D. in July 1921 for his thesis on the quantum theory of ionized molecular hydrogen under his doctoral adviser Arnold Sommerfeld.

Pauli was influenced by Bohr’s lectures in understanding the concept of atomic model. The question, as to why all electrons for an atom in the ground state were not bound in the innermost shell, that Bohr tried to answer has no convincing explanations during his lectures in Gottingen. Pauli’s eager to answer the question also led to answer another phenomenon. He was in Copenhagen when he made a serious effort to explain the formation of douplet-spectra of the alkali metals spectra for which they called the Anomalous Zeeman Effect. This type of splitting exhibited of the spectral lines in a magnetic field is different from the normal triplet by normal Zeeman Effect. The reason of Bohr was that a non-vanishing angular momentum of the atomic core was supposed cause of this douplet structure. Pauli argues with this reason which he rejected and instead of it he proposed a new quantum theoretic property of the electron, which he called a “two-valuedness not describable classically”. The idea of electron spin were introduced by Uhlenbeck and Goudsmit, which made Pauli understand the anomalous Zeeman effect by simply assuming a spin quantum number of one electron is equal 1/2. Since then, idea of exclusion principle has been closely connected with the idea of spin. The idea of spin is then become essential to quantum-mechanical property of electron and to the field of quantum mechanics. Hence, exclusion principle states that no two electrons can occupy the same quantum or energy state of an atom simultaneously.

Local realism is the idea that an object has definite properties or assumes a definite state without being affected by the act of measurement [1]. This belief is especially contrary to the probabilistic ( not deterministic ) characteristic of quantum mechanics.

In 1965, John S. Bell had proposed a mathematical proof or designed several experiments that would test the consistency of quantum mechanics, and hence the inconsistency of the local reality. This has brought the idea that quantum mechanics is an incomplete theory. That is, physical properties such as momentum and position were absolute values and that when they exist, whether they were measured or not, an inequality ( Bell’s inequality), would then be satisfied. But later on this theory was the subject of considerable interests and debates, and loopholes are uncovered by the much refined experiments. Moreover, several proposals for closing this loophole have been made as well, and previous investigation was reported.

Early experiments such as the experiment in the correlation measurements in the classical properties of massive entangled particles Be⁺ ions, were made to test Bell’s inequalities and these were subject to two primary loopholes. The first primary loophole might be termed as ‘locality’ or ‘lightcone’ loophole, in which the correlations of apparently separate events, could result from unknown subluminal ‘signals’ propagating between different regions of the apparatus. These correlations violate a form of Bell’s inequality which was obtained by a complete set of measurements. Here, the appropriate ‘Bell’s signal’ is  2.25 +/- 0.03, whereas a value maximum of 2 is the only allowable value by local realist. Similar results have also been reported for the Geneva experiment [2]. The second loophole is usually referred to as the detection loophole. Here, every experiments is assumed to have had detection efficiencies low enough to allow the possibility that the sub-ensemble of detected events agrees with quantum mechanics even though the entire ensemble satisfies Bell’s inequalities. Conversely saying, the detected events thus represent the entire ensemble; a fair-sampling hypothesis. Thus, in the presence of an ‘accurate set’ of measurements, Bell’s inequalities are violated. Meaning, as a way of eliminating the so-called “detection-loophole”, more high-detection efficiency experiments were designed that would put distinction between what local realism is, and when the quantum mechanics theory should be applied.

[1]  M.A. Rowe, D. Kielspinski, V. Meyer, C.A. Sackett, W.M. Itano, C. Monroe, and D.J. Wineland. Experiemental violation of a Bell’s inequality with efficient detection. Letters to nature. Nature 791, Vol 409 (2001)

[2]  Tittel, W., Brendel J., Zbinden H. and Gisin N. Violation of Bell’s Inequalities by photons more than 10 km apart. Phys. Rev. Lett. 81, 3563-356 (1998)

“Schrodinger’s cat paradox is a classical illustration of the conflict between the existence of quantum superpositions and our real-world experience of observation and measurement”[1].

The Principle of Superposition of States in quantum mechanics has become strikingly successful at describing physical phenomena at the atomic scale.  Quantum superposition requires us to assume that between states there exists a peculiar relationship such that whenever the system is in one state we can consider it as partly in the other states.

Now, what if we extend quantum superposition to macroscopic systems? This is where the Schrodinger Cat comes to the picture.

Schrodinger Cat started out to be a thought experimenent: An unfortunate cat is placed in a quantum superposition of being dead and alive.  How was this done? simply put, a cat was placed in a box together with a single radioactive atom that has and has not decayed.  The state of the system can be represented by the entangled quantum mechanical wave function:

where and refer to the states of a live and dead cat, and and refer to the internal states of an atom that has and has not radioactively decayed.  We know that if the atom has not decayed the cat is alive and dead otherwise; but of course if we open the box, we only observe a live or dead cat and not both states.

Although it is quite impossible  for a Schrodinger’s cat (SC) to exist in the macroscopic world, there is great interest in creating SC-like states in mesoscopic systems, or systems that have both microscopic and macroscopic features.  SC-like states may provide a testing ground for the controversial theory of quantum measurement and the universality of the quantum theory.

The SC-like state was created by forming a superposition of two coherent-state wave packets of a single trapped atom with a sequence of laser pulses.  Each wave packet is correlated with a particular internal state of the atom.  A ion was confined in a coaxial-resonator radio frequency trap that provides the harmonic oscillator frequencies.  The ion was laser cooled to the zero point energy and then its internal (electronic) and external (motional-nearly classical) state was coherently manipulated by applying pairs of off-resonant laser beams.  The SC superposition was verified by detection of the quantum mechanical interference between the localized wave packets[1].  The downside of the experiment is when the SC state is coupled to a thermal reservoir the superposition decays exponentially into a statistical mixture, that is the lifetime of the superposition shortens.  This phenomenon is called decoherence which explains why superpositions are rare if not impossible in the macroscopic scale, and illustrates the difficulty in preparing and maintaining even mesoscopic superpositions.

[1]C. Monroe, et. al. A “Schrodinger Cat” Superposition State of an Atom

About the author:

Sandra Manulat is taking her master’s degree in physics at MSU-Iligan Institute of Technology.  She aspires to become a physicist her country could be proud of.

Quantum mechanics is one of the most functional theories in the world of physics.  It describes the workings of particles, atoms, and molecules with extraordinary accuracy and also explains the action of lasers and transistors. Yet, the debate about the relation of quantum mechanics to the familiar physical world continues.

For instance, the so-called measurement problem has been a source of continual speculation. In quantum mechanics, it is the unresolved problem of how the wavefunction collapses. The wavefunction obeys the deterministic Schrödinger equation into a linear superposition of different states. However, actual measurements always find the physical system in a definite state. But why we cannot predict precise results for measurements, but only probabilities?

The Copenhagen interpretation which is proposed by Niels Bohr was the first accepted explanation of how a single outcome emerges from the many possibilities and insisted that a classical apparatus is necessary to carry out measurements.  It created a dividing line between classical and quantum. The border line must be mobile according to Niels Bohr. Classical is identified frequently as macroscopic but the insufficiency of this approach has become visible as a result of recent developments such as the cryogenic version of the Weber bar, a gravity wave detector which must be treated as a quantum harmonic oscillator even though it can weigh a ton.

There might be no boundary between classical and quantum since macroscopic systems cannot always be safely placed on the classical side of the boundary. The many-worlds interpretation claims to do away with the boundary. In this interpretation, the superpositions evolve without end according to the Schrodinger equation. Zurek stated that “Each time a suitable interaction takes place between any two quantum systems, the wavefunction of the universe splits, so that it develops ever more branches.” Hugh Everett, the author, proposed the idea that the wavefunction never collapses. The many-worlds interpretation and other post-Everett interpretations use decoherence to explain the process of measurement or wavefunction collapse.

Decoherence try to clarify the transition from quantum to classical by analyzing the interaction of a system with a measuring device or with the environment. It can be viewed as the loss of information from a system into the environment. As Stahlke said, “any interaction with the environment leads to an entanglement between the particle’s state and the environment’s state. As the entanglement diffuses throughout the environment the total state can no longer be separated into the direct product of a particle state and an environment state.”

Although decoherence does not give the solution in the measurement problem but it does bring some enlightenment. It is still unknown at which point the wave actually collapses and caught the attention of the scientific world. Environmental entanglement provides a mechanism in which wave collapse can transmit into the system from distant.

[1.] Zurek, Wojciech H. Decoherence and the Transition from Quantum to Classical. Physics Today. October,1991.

[2.] Stahlke, Dan. Quantum Decoherence and the Measurement Problem

For many years, computers have doubled in power every year or so, as what Moore’s law predicts. This means that transistors are getting smaller and smaller and will eventually approach the size of an atom. However, in the atomic regime, the physics is completely different from what is observed in the electronic devices of today. In this level we have to consider the strange effects of quantum mechanics (QM).

In the classical model of a computer, the most fundamental building block of information, the bit, can only exist in one of two distinct states, a 0 or a 1 encoded in electronic components such as transistors. A bit is analogous to a head and a tail of a coin. When you toss a coin you can only have one of the two states. However, for a quantum computer, a quantum bit or a ‘qubit’ does not follow these rules. A qubit can be 0 or 1 or 0-1 or 0+1 or 0 and 1, all at the same time! This is where quantum mechanics comes in, i.e., the principle of superposition of states. Such superposition of states can lead to a simultaneous processing of 2^N values that are being expressed simultaneously by N qubits. This allows far greater flexibility than the binary system. This means that more qubits you have, more options you can work with, thus, the faster you go.

We may now ask, What is the best way of creating a quantum computer or giving a system a qubit form? Physically, qubits are encoded in ions, photons, atoms/molecules, or electrons. Different qubit systems have its advantages and disadvantages. For instance, charged particle or ion trapped within an electromagnetic field or trapped using optical techniques can serve as a qubit however it is vulnerable from decoherence. It is very much important for a quantum computer to isolate the qubit because any interactions from the environment destroy the superposition of states thus causing decoherence or loss of its quantum character. Now, for a molecule, the up and down directions of the nuclear spin can also act as a qubit. Nuclear spins make excellent quantum memory since they interact with their environment only via their tiny magnetic fields. However, for the same reason, this makes the quantum information hard to access. On the other hand, photons can also be fast and robust carriers of quantum states encoded in polarization state thus making them a good medium by which to transmit quantum information. However, these attributes also mean that they are difficult to localized and store. Another approach is by using a solid state device, either a qubit achieved by a superconducting circuit using the Josephson junction or a qubit achieved by a semiconductor quantum dot. Quantum bits encoded in states with different electrical charges can be manipulated and measured very rapidly but the charges make short-lived qubits since they are strongly coupled to their local electrical environment.

Another problem with quantum computing is that if you observe or measure the quantum state of a qubit, it changes its value. So scientists must devise an indirect method of determining the state of a qubit, that is, by taking advantage of another quantum property called “entanglement.” At the quantum level, if you apply a force to two particles they become “entangled” meaning, a change in the state of one particle is instantly reflected in the other particle’s change to the opposite state. So by observing the state of the second particle, physicists hope to determine the state of the first. Thus, quantum effects can be used to acquire information about the system.

A working quantum computer should contain thousands of qubits in order to solve real-world problems usefully. One must have a technology that enables quantum systems to exist as coherent states for a long period of time. Various methods are being experimented and give promising results. One solution is to use a hybrid approach known as quantum network to maximize the different qubit systems. Basically, this approach involves the transfer of quantum information from one qubit form to another. For instance, quantum states which are stored and manipulated in matter qubits are mapped into photons for long distance transmission. The challenge now is to develop techniques in order to coherently morph quantum bits from matter to light.

So, what is the big deal with the quest for high speed computing and quantum computation? Actually, Mother Nature has endowed us with physical phenomenons which are way way too far complicated to solve using conventional computing. For example, we may want to know the ground state of a particular homogeneous system, such as an array of mutually coupled identical spins, or measure simple correlations between different parts of the system. This will pave the way to understanding condensed-matter systems and understanding of materials such as high-temperature superconductors. Not only that, by using algorithms such as Shor’s algorithm, a quantum computer would be able to crack codes much more quickly than any ordinary computer could. Breaking such encryption standards can however put one’s security at risk. Another breakthrough if quantum computing would be a success is the creation of computers that would be capable of simulating conscious rational thought – the key to achieving true artificial intelligence.

As of now, baby steps were made towards the goal of large scale quantum computers. The future of quantum computing is very promising but the benefits must outweigh the risks it could bring.