A team of researchers from Stanford University has been investigating some new materials that they believe will bring us closer to building practical quantum computers.
Building Quantum Computers
One possible way to build quantum computers would be to use lasers to isolate spinning electrons inside a semiconductor material. When the laser hits the electron, it shows how the electron is spinning by emitting one or more light particles. The spin states can then be used as the most fundamental building blocks for quantum computing, the same way conventional computing uses 1s and 0s.
According to Stanford electrical engineering Professor Jelena Vuckovic, who has been investigating these new materials to build quantum computers, quantum computing would be ideal for studying biological systems, doing cryptography, or data mining, as well as for any other complex problem that can’t be solved by conventional computers.
“When people talk about finding a needle in a haystack, that’s where quantum computing comes in,” said Vuckovic.
The challenge in isolating spinning electrons is finding a material that can confine the electrons when the lasers hit them. Vuckovic’s team has identified three materials that can potentially do this: quantum dots, diamonds, and silicon carbide.
A quantum dot is a small amount of indium arsenide inside a crystal of gallium arsenide. The atomic properties of the two materials are known to trap spinning electrons.
In a recent paper, Kevin Fischer, a graduate student in the Vuckovic lab, described how the laser-electron processes can be used within a quantum dot system to control the input and output of light. For instance, by applying more power behind the lasers, two photons could be emitted instead of one. This could be used as an alternative to the 1s and 0s of conventional computers.
One issue is that the quantum dot system still requires cryogenic cooling, which doesn’t make it a suitable candidate for general-purpose computing.
Diamond Color Centers
Vuckovic’s team has also been investigating modifying the crystalline lattice of a diamond to trap light in what is known as a color center. The team replaced some of the carbon atoms in the diamond’s crystalline lattice with silicon atoms.
Like the quantum dots approach, doing quantum computing within diamond color centers requires cryogenic cooling.
Silicon carbide is a hard and transparent crystal that is used to make clutch plates, brake pads, and bulletproof vests, among other things. Prior research has shown that silicon carbide could be modified to create color centers at room temperature, but not in a way that’s efficient enough to create a quantum chip.
Vuckovic’s team was able to eliminate some of the atoms in the silicon carbide lattice to create much more efficient color centers. The team also fabricated nanowires around the color centers to improve photon extraction.
Trapping electrons at room temperature could be a significant step forward for quantum computers, according to Vuckovich. However, she and her team are also not sure which method to create a practical quantum computer will work best in the end.
Some of the biggest technology companies in the world are working on building quantum computers right now, including Google, IBM, and Microsoft. Teams at many universities around the world are also experimenting with different approaches to building quantum computers.
Both Google and IBM believe we’ll reach “quantum supremacy”--the point when quantum computers will be faster than conventional computers at solving a certain type of complex problems--when quantum computers have around 50 qubits (from the fewer than 10 qubits they do now). The two companies expect this goal to be reached in the next few years.