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Could you elaborate on "repurpose silicon fab technology"? I know pretty much nothing about quantum computing. How does the manufacturing process differ?

mathgenius 10y ago
The attempts to build "qubits" involve very complicated custom gadgets, with strange crystals or superconductors, or other weird things I don't know much about. And then refrigerated down to almost absolute zero. And it's not just about mass producing qubits, they need to talk to each other, ie. be entangled. And that is the really hard part about all of this.
ThePhysicist 10y ago
Most superconducting qubits, such as the "Transmons" used by Google and various other labs are made of Aluminium, as this is a material which has good properties and can be easily deposited using e.g. evaporation-based methods (i.e. heat Aluminium in a vacuum so it evaporates and gets deposited on the surface of a chip that you put nearby). The microwave circuits on the chips are typically made out of Niobium (another superconductor), which is not very suited for making qubits but which provides very good properties for building large-scale structures such as coplanar waveguides. To fabricate a qubit, normally one first deposits Niobium on a Saphire/Silicon wafer and then etches structures into this using photo lithography. Afterwards, the Aluminium qubits get deposited using so-called shadow evaporation technique, where you create two layers of Aluminium separated by a thin insulating barrier that is created by first depositing a single layer of Aluminium, oxidizing it and then depositing another layer of Aluminium at a different angle. This process is quite finicky and the yield of working qubits you get out of it is (or at least was at the time I worked on this) rather low. Adapting techniques from conventional semiconductor manufacturing (were error rates are < 1^-9 per transistor) seems therefore very promising. So far it seems that there are still many hurdles to overcome for this, though the fabrication methods get more reliable every year.

mathgenius 10y ago

The attempts to build "qubits" involve very complicated custom gadgets, with strange crystals or superconductors, or other weird things I don't know much about. And then refrigerated down to almost absolute zero. And it's not just about mass producing qubits, they need to talk to each other, ie. be entangled. And that is the really hard part about all of this.

ThePhysicist 10y ago

Most superconducting qubits, such as the "Transmons" used by Google and various other labs are made of Aluminium, as this is a material which has good properties and can be easily deposited using e.g. evaporation-based methods (i.e. heat Aluminium in a vacuum so it evaporates and gets deposited on the surface of a chip that you put nearby). The microwave circuits on the chips are typically made out of Niobium (another superconductor), which is not very suited for making qubits but which provides very good properties for building large-scale structures such as coplanar waveguides. To fabricate a qubit, normally one first deposits Niobium on a Saphire/Silicon wafer and then etches structures into this using photo lithography. Afterwards, the Aluminium qubits get deposited using so-called shadow evaporation technique, where you create two layers of Aluminium separated by a thin insulating barrier that is created by first depositing a single layer of Aluminium, oxidizing it and then depositing another layer of Aluminium at a different angle. This process is quite finicky and the yield of working qubits you get out of it is (or at least was at the time I worked on this) rather low. Adapting techniques from conventional semiconductor manufacturing (were error rates are < 1^-9 per transistor) seems therefore very promising. So far it seems that there are still many hurdles to overcome for this, though the fabrication methods get more reliable every year.