Impact of Classical Control Electronics on Qubit Fidelity

Abstract

Quantum processors rely on classical electronic controllers to manipulate and read out the quantum state. As the performance of the quantum processor improves, non-idealities in the classical controller can become the performance bottleneck for the whole quantum computer. To prevent such limitation, this paper presents a systematic study of the impact of the classical electrical signals on the qubit fidelity. All operations, i.e. single-qubit rotations, two-qubit gates and read-out, are considered, in the presence of errors in the control electronics, such as static, dynamic, systematic and random errors. Although the presented study could be extended to any qubit technology, it currently focuses on single-electron spin qubits, because of several advantages, such as purely electrical control and long coherence times, and for their potential for large-scale integration.As a result of this study, detailed electrical specifications for the classical control electronics for a given qubit fidelity can be derived, as demonstrated with specific case studies. We also discuss the effect on qubit fidelity of the performance of the general-purpose room-temperature equipment that is typically employed to control the few qubits available today. Ultimately, we show that tailor-made electronic controllers can achieve significantly lower power, cost and size, as required to support the scaling up of quantum computers.

Semiconductor quantum computation

“…Now that high fidelity control and readout of single-and two-qubit gates in semiconductor have been demonstrated, the next challenge lies in how to scale it to tens and hundreds of qubits. Corresponding constraints and problems were investigated thoroughly since 2015, including the geometry and operation time constraints [177,178], engineering configuration for quantum-classical interface [179][180][181][182], and even the quantifying of system extensibility [183]. In the light of these discussions, several proposals for scaling up were proposed, varying from the crossbar network [38,39] for spin-1/2 qubits in silicon MOS quantum dots, the two dimensional lattice of donor qubits in silicon [35,36], to the hybrid architecture like donor-dot structure [37] and flip-flop qubit structure [113].…”

The electronic interface for quantum processors

“…In summary, the performance of the analyzed setup is sufficient to drive single-qubit operations in an ideal quantum processor with a 99.9% fidelity. More in general, it can be concluded that typically adopted general-purpose instruments are not limiting the fidelity of state-of-theart quantum computers, as shown in [60], since solid-state semiconductor qubits with fidelity exceeding 99.9% have been only recently demonstrated [73]. While this situation is desirable for current developments focused on improving the performance of quantum processors, the large performance margin in the electronic interface may not be tolerated as the performance and the scale of quantum processors improve, as discussed in Section 4.…”

“…The effect of signal non-idealities can be either simulated [58] or analytically evaluated [59,60]. As an example, the sources of inaccuracy and the related specifications of the microwave pulse that achieves a 99.9% fidelity for a π-rotation on a single-electron spin qubit are shown in Table 2.…”

“…The interested reader is referred to Ref. [60] for a complete analysis of the electrical specification for single-electron spin qubits, which shows a methodology that can in principle be adapted to any qubit technology.…”

Cryogenic Characterization of 28-nm FD-SOI Ring Oscillators With Energy Efficiency Optimization

“…Furthermore, the energy efficiency of a cryogenic platform for the classical control of a scalable quantum computer is essential. Low power dissipation is required, down to few watts at 4K [24] to enable Fig. 5.…”