An exciting triumph in nanotechnology has brought us one step closer to a quantum computing reality: scientists at the University of New South Wales in Sydney have successfully constructed a working transistor out of a single atom of Phosphorous deposited on a silicon substrate.
While single atom transistors aren’t an outright new creation, previous iterations have been stumbled upon by accident and the responsible scientists have been unable to replicate their results with any amount of certainty. The team, led by Professor Michelle Simmons, touts their single atom transistor as being the first that can be reliably created with atomic precision, which has profound implications for possible commercial production.
How Did They DO That??
The device was constructed using a combination of scanning tunneling microscopy and Hydrogen lithography. First, a very smooth silicon substrate can be mapped by measuring small variations in current as a fine metal tip is moved across the top layer of silicon atoms on the substrate surface. A single layer of Hydrogen atoms is deposited across the top of the silicon, and then single Hydrogen atoms can be removed by manipulating with precise pulse voltages. Phosphine gas is introduced to the reactive dangling Hydrogen bonds, and the result is a placement of a single Phosphorous atom to an unprecedented amount of accuracy. Once the Hydrogen is removed and the Phosphorous is encapsulated by more silicon and electrodes are attached to the ends of the atom, it becomes a working quantum transistor.
Keeping Up With The Mooreses
Atomic transistors are the holy grail for computing enthusiasts eager to keep up with Moore’s Law, which states that computing power doubles every 18 months (and has held true for about 50 years). Gordon Moore, for whom the law is named, believed that the limit of his theory existed in the quantum world, at which point it becomes physically impossible to fit more transistors into a defined space. This achievement sets us on a path to come in early against the predicted emergence of single-atom-based computers in 2020.
The Big Cost of Small Size
But don’t start high-fiving your physicist friends just yet: technology like this, especially in its early phases, comes at a high price tag. The equipment necessary to create the kind of environment that made production of this single-atom device possible is expensive to buy and to operate, and this doesn’t yet include the steps taken to design the lab itself. Professor Simmons mentions in her description of scanning tunneling microscopy technology that many of the failures seen by previous explorers in the field have been due to vibrations from the vacuum chamber pumps interfering with the nearby imaging equipment. As a result, the high vacuum equipment in her lab is placed on a concrete slab that floats independently of the building that houses the imaging technology next-door, and she estimates the cost of her project to be upwards of $3 million.
A paradigm shift from the classical regime to quantum programming would also mean a complete change in the way we think about software, as all current processors are based on transistors being able to occupy one of two states: 1 or 0, on or off. Quantum bits, or qubits (qbits), can occupy a range of states, as the state is based on electron spin. If quantum computing becomes a reality, it could in theory exponentially increase the speed at which we’re able to process data.
Professor Michelle Simmons describes the technology behind the single-atom transistor in the video below.