A Mixed-Signal Control Core for a Fully Integrated Semiconductor Quantum Computer System-on-Chip

This paper discloses a mixed-signal control unit of a fully integrated semiconductor quantum processor SoC realized in a 22nm FD-SOI technology. Independent high-resolution DACs that set the amplitude and pulse-width of the control signals were integrated for each qubit, enabling both a programmable semi-conductor qubit operation and a per-qubit individual calibration that compensates for the process variability. The lower decoherence time of the semiconductor charge-qubits as compared to their spin-qubit counterparts was mitigated by using a high frequency of control unit operation. This is facilitated by the co-integration on the same die of the semiconductor quantum structures together with their corresponding classic control circuitry. The main challenge of achieving deep cryogenic operation for the mixed-signal classic control circuit was surpassed by using programmable local heating DACs that slightly boost the local temperature of the control blocks above the average temperature of the die, which needs to be maintained around 4 K to enable a reliable quantum operation. A staged multi-phase operation was adopted for the digital core in order to minimize the quantum decoherence originated in digital noise injection. The high-frequency clock tree and divider allows the generation of sub-20 ps fast edge control pulses with programmable widths down to 166 ps. This offers a wide quantum computation window when compared with the 1 mu s decoherence time of the charge-qubit structures.