First Quantum Implementation of Von Neumann Architecture Achieved, Large Quantum Computers Next Stop!
By on September 2nd, 2011

The first quantum version of the Von Neumann architecture has been implemented by physicists at University of California, Santa Barbara (UCSB). This represents a crucial step in the creation of quantum computers which will make calculations at least a million times faster. The micro quantum computers are already here!

The implementation of the von Neumann machine on the quantum scale. Courtesy: UCSB

Why such a big deal?

Kindly realise the magnitude of the achievement. The Von Neumann architecture, partly developed and articulated by mathematical genius John von Neumann, is the principal methodology used in building the hardware and supporting software in computers. The architecture came into existence in the 1940′s due to the work of Von Neumann and Alan Turing. Since then, it has formed the bedrock of computer hardware design, even though there have been many improvements on it. However, the architecture has been realised only with classical computers, or computers whose bits are macroscopic physical objects. It has been a major challenge for computer scientists to either build up the quantum analogue of the Von Neumann architecture or to implement using quantum systems.

What is the Von Neumann Architecture?

Here’s what the Von Neumann architecture is. Every Von Neumann machine is made up of four units the Arithmetic-Logic Unit, the Memory, the Control Unit and the Interface. The architecture prescribes that instructions be also stored in the memory, rather than just data. In fact Von Neumann prescribes that the instruction code be stored exactly like data. In response to the code, the data changes and produces intermediate computation results, finally ending up with the end result. The key feature is that the instructions themselves be pliable. They should change with the data i.e. they are self-modifying. They can be encoded in numeric form, just like data, so that this can be achieved. These instructions are then pulled’ up from the memory. Two types of buses’ or data trains link the various components of the Von Neumann machine the data bus and the address bus. The rate at which these buses can transfer data puts a theoretical upper cut-off. This is the von Neumann’ bottleneck.

Realise that the Von Neumann architecture is contradictory to the structure of modern high level languages, where you have definite separation of the data and the instruction code.

Quantum Implementation: Using Qubits

The circuits developed by the UCSB physicists use superconducting quantum circuits, which require extremely low temperatures to operate. The demonstration of the fact that this can be done implies that quantum computing can indeed be achieved on a macroscopic scale. Dreams of Large Scale Integration (LSI) or Very Large Scale Integration (VLSI), achieved long ago with conventional computer components, are not very far-fetched either!

VLSI on the quantum scale?

The key to the quantum implementation of the Von Neumann architecture is quantum bits or qubits. Unlike the classical bit, which can be in either 1 or 0 state, qubits can exist in a superposition of many quantum states, allowing for many more calculations to be done on a single qubit simultaneously. The fundamental unit of a quantum computer comprises two qubits, a quantum communication bus, two bits of quantum memory and a resetting counter. This uses Von Neumann architecture on the nano scale!

The aim of simultaneously writing information to the quantum memory and performing quantum calculations on the qubit has not been achieved, but scientists are close to that. The three-qubit Toffoli gate has already been implemented.

Super-fast calculations, here we come!

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Author: Debjyoti Bardhan Google Profile for Debjyoti Bardhan
Is a science geek, currently pursuing some sort of a degree (called a PhD) in Physics at TIFR, Mumbai. An enthusiastic but useless amateur photographer, his most favourite activity is simply lazing around. He is interested in all things interesting and scientific.

Debjyoti Bardhan has written and can be contacted at debjyoti@techie-buzz.com.

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