Quantum systems in contest
There are various approaches to developing quantum computers, each of which has its advantages and disadvantages. At present, it’s still anyone’s guess as to which system will ultimately prevail. In the following, we present an overview of the most promising technologies.
Photons
Photons—or light particles—are guided through the processor in so-called waveguides. The photons are linked and then manipulated using optical components or photodetectors. Photon-based qubits don’t require extreme cooling. However, the interaction between the photons is low, and the programmability of these “flying qubits” is limited.
Superconducting circuits
Superconducting circuits consist of superconducting wires through which electricity flows back and forth at zero loss. Qubits are induced and manipulated using microwave pulses, enabling operations to be conducted very quickly. However, the qubits also collapse again rapidly. Another disadvantage of the method is that the circuits must be cooled to temperatures approaching absolute zero—minus 273.15 degrees Celsius.
Ion traps
In ion traps, ionised atoms or molecules are captured and then manipulated using electromagnetic fields and lasers. The resulting qubits are extremely stable and can be controlled with high precision. The drawback, however, is that computations with trapped-ion qubits are very slow. In addition, researchers have not yet managed to place a large number of these qubits on a single chip.
Quantum dots
Electrodes generate an electric field in semiconductors in which individual electrons can be trapped. There, in these quantum dots, microwaves can be used to control the particles’ spin states. A major advantage of this method is that it builds on already existing semiconductor technology. However, quantum dots must be cooled to almost absolute zero, and they require extremely pure materials.
Diamond lattice
Foreign atoms—and with them, an additional electron—are directly inserted into artificially grown diamond lattices. The electron’s spin state can be controlled via a laser. Diamond qubits are compact and can be operated at room temperature. However, generating and combining a large number of qubits remains an unresolved challenge.
Neutral atoms
This method involves trapping atoms that have balanced charges and manipulating them using bundled laser beams that slow the atoms down until they can hardly move. These kinds of platforms are very easy to scale and don’t require use of a cryostat—a low-temperature cooling device. The problem is that the qubits are susceptible to interference, and they rely on complex laser techniques and set-ups.
