The solace of quantum

Building a quantum computer
So we've now got a very superficial handle on what a quantum state is and what quantum phenomena are composed of. Why can't we just go and build a quantum based computer? To answer that, we will investigate how they are constructed and engineered to begin with.

The complex states in which quantum computing can exist are currently only calculable and attainable in a laboratory environment. The reason these states are only observable and controllable in a laboratory environment is because of the nature of atomic (and sub atomic) interactions. Think tiny. <i>Really</i> tiny.

A way to represent these really tiny states, and the previously mentioned ability to exist in multiple states simultaneously is to use a Bloch Sphere (pictured above). 

Originally named after the physicist Felix Bloch, the Bloch Sphere is a physical representation of a two state quantum system. It could be considered a 1-bit quantum register, akin to that of our binary-based registers, as we know them in traditional computing.

The pairs of antipodal points on the Bloch Sphere represent the pairs of states of a particle. These pairs and their 'neither here nor there' existence represent spin-up and spin-down. It is these pairs, as the formation of a qubit that are the building block of the quantum calculation, and ultimately, the quantum computer.

By now, you've gotten the hint that a quantum system works on an atomic scale. To isolate atomic particles and make them do as we wish (and perform calculations with them), there are several mechanisms in place that quantum-computing engineers and researchers are using.

• Ion traps - an optical or magnetic field to trap ions.
• Optical traps - using light to trap and control particles.
• Quantum dots - semiconductor based materials that can contain and manipulate electrons.
• Superconducting circuits - allowing electrons to flow with virtually zero resistance (and then to be corralled) at extremely low temperatures.

In the most pure form, most of the quantum computers in existence only manipulate between 16 and 384 qubits, with the majority of the experimentation taking place being purely theoretical. This being said, there are several quantum devices capable of 'computing' being engineered and tested around the globe.

Perhaps the closest the world has come to a marketable, reproducible and ready-engineering quantum computing solution are the superconducting processors from the company D-Wave. The approach D-Wave or 'The Quantum Computing Company' has taken in engineering a superconducting microprocessor is one of algorithm intelligence. The core engine theory is to be able to compute adiabatic quantum algorithms. The concept of an adiabatic algorithm is deeply rooted in a branch of physics known as Hamiltonian mechanics, which involves known ground states, where the total amount of potential and kinetic energy of a quantum system can be used to understand or describe solutions to problems.

In an adiabatic algorithm, a quantum system subjected to gradually changing external conditions (the movement or modification of a qubit in a register to perform a calculation, for example) has the ability to adapt its functional form if changes occur slowly enough.

A real world, physical example of this is a simple pendulum rocking back and forth in a vertical plane. If somebody comes along and moves the support for it, the oscillation of the pendulum rocking back and forth will change. If the support is moved sufficiently slowly, the motion of the pendulum object relative to the support will remain unchanged. A gradual change in conditions allows this system to adapt, and as such, it retains initial capabilities, performance and character. This is the core explanation of an adiabatic quantum process.

D-Wave's new shiny beast is capable of 128 qubit manipulation - stored on 128 superconducting niobium loops as either clockwise or anticlockwise current, representing 0 or 1 - or as a qubit with both currents at the same time in a quantum superposition. When processing is required, the niobium-based qubits are manipulated and configured using a magnetic field.

Its one thing to build a niobium spinning magnetically shielded device that has the ability to focus the spin of any given ions around an atom, but it's another entirely to keep the environment around it sane for the purposes of useful calculations.  Much of the time, extreme cooling requires significant energy sources, and on top of this, isolated (conventional) computing control facilities.