Maximum Micro Tech: Three New Technologies Explained

Posted 12/08/2011 at 12:50pm | by Zack Stern and Bill O'Brien

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Quantum Computing

In the future, we'll ditch binary bits for decidedly nonbinary qubits. The end result will revolutionize computing

Despite the misconception created by phrases such as "quantum leap," quanta are among the smallest known particles in the universe. If they weren't, quantum computing wouldn't be such a big deal.

At its core, quantum computing leverages the possible dimensions associated with the quantum properties of a physical atom. The construction of a quantum computer involves the arrangement of entangled atoms. A quantum entanglement is a description of the state of a system containing two or more objects. The objects within wuch a system are associated in such a way that the quantum state of any one of them cannot be adequately described without full mention of the others—even if the objects are separated from each other.

If that's starting to sound a bit complex, you're probably an Einstein devotee. He and a few friends (Podolsky and Rosen, to name two), postulated that all physical objects have real values at all times. Unfortunately, thanks to the behavior of particles on the atomic level, that's not necessarily the case for quantum computing.

Parts is Parts

The core of a quantum computer starts with a quantum bit, or qubit as it's more often called. The qubit is the fundamental equivalent of the digital computing "bit." However, while a bit must be be either 1 or 0, a qubit can be either |0> or |1> (for the purposes of quantum computing, the added notation indicates that the object can be a state, a vector, or a ket).

To visualize the possible states of a single qubit we typically use a Bloch sphere. Within such a sphere, because of its on/off nature, a classical bit could only be at the "north pole" or the "south pole," in the locations where |0> and |1> are positioned, respectively. The rest of the surface of the sphere is inaccessible to a classical bit but not in the case of a qubit. A qubit state can be represented by any point on the surface—any point. For example the pure qubit state:

|0> + i|1>
√2

would lie on the equator of the sphere, on the positive y axis.

Computing on the Quantum Level

A quantum computation is performed by initializing this system of qubits with a quantum algorithm. "Initialization" here refers to some process that puts the system into an entangled state.

How to do that? In a natural state, sub-atomic particles decay into other particles. The decay follows the atomic laws of convservation and you can, therefore, generate pairs of particles that will be in certain predictable quantum states.

Purposefully initializing such a system typically entails one of the following methods: using spontaneous parametric down-conversion, where a nonlinear crystal is used to split incoming photons into pairs of photons of lower energy; using a fiber coupler to confine and mix photons; or using a quantum dot, a semiconductor whose excitons are bound within all three spatial dimensions, giving it properties that are somewhere between those of bulk semiconductors and those of discrete molecules, to trap electrons until decay occurs.

Typical computational gates use Boolean logic, but in quantum computing, these gates are represented by matrices, and can be thought of as rotations of the quantum state within a Bloch sphere (see the infographic below).

This Bloch sphere is the typical representation of a qubit and indicates its possible states. A typical bit would have states on the north and south poles of the sphere. A qubit's state can be represented by any point on the surface.

Manipulating these states presents the probability of performing a mathematical operation on all of a qubit's states simultaneously. For example, as a single qubit state can be 1 and 0 or 0 and 1, we could compute four values at once using two qubits. Doubling that to four qubits pushes the possibility to 16 values, and so on. The more you increase the number of qubits, the more the processing power increases in an exponential fashion. It's akin to the way we started back in the dark ages with 4-bit, then 8-bit, then 16-bit processors until now we've reached 64-bit (on the desktop at least). Here as there, increasing the number of bits increases the data precision as well as the amount of data the CPU can handle in one fell swoop.

Is Quantum Computing Practical?

While the first quantum processor was built back in 2009 by a team out of Yale University, a useful quantum computer is still at least that ubiquitous 10 years (if not further out to 50 years) away. Early quantum algorithms tried to exploit very simple quantum computing, using what's called "oracles." Like a Magic 8-Ball, they were designed to deliver yes or no answers. That's hardly adequate for even our most basic binary computer of today.

Beefing up a quantum computer is not simple. The overall goal is to stay small, but just the logic gates alone are a serious point of consideration. A 16-qubit computer can register a single "NOT" gate. Now imagine the possibilities beyond that.

We might be able to cure some of the clutter if we use ternary computing lessons (three possible values as opposed to transferring binary technology, which uses bits) that employ "trits" to store data. With this method, it may be possible to transfer this concept over to quantum computing with a roughly equivalent qutrit. That lone would reduce the number of gates significantly, possibly lowering a 50-gate construct down to one needing only nine gates.

Coherence is another hurdle. Simply looking at a qubit (or in any other way letting it interact with the environment) will cause it to decohere or dephase. Decoherence impedes superimposition, which reduces the quantum computer's effectiveness—sometimes down to binary levels.

Still, however, once these impediments have been conquered, over whatever time period it might take, a quantum computer could tackle password and encryption problems, as well as simulations and design tasks, in a matter of heartbeats, where a conventional binary computer might require a lifetime. That's what makes them so magical.