Universal quantum computation requires single-qubit control together with at least one entangling two-qubit gate. CNOT and CROT gates are two famous examples of such gates, wherein the state of one qubit (control) dictates the transformation applied to the other (target). By using a simple derivation motivated by symmetry, we show that current device architectures of semiconductor-based quantum dot devices prevent efficient implementation of a CNOT and other asymmetric control-target gates via Heisenberg exchange, Coulomb repulsion, or other interaction that is invariant under spin exchange. Guided by this general principle, we propose a heterogeneous blueprint of double quantum dot devices that enables efficient implementation of the CNOT by breaking the spin exchange symmetry. Crucially, our numerical simulations predict that this novel device blueprint can enable a single-pulse fault-tolerant 100-ns CNOT gate in isotopically purified silicon.
Quantum error correction (QEC) is beginning to enable logical operations that outperform their unencoded physical counterparts, but useful fault-tolerant computation will require more than low-error quantum memory. An effective architecture must orchestrate efficient logical encoding, low-overhead logical operations, and access to the non-Clifford resources required for universal computation. Here, we introduce and experimentally validate such an architecture based on the
[[20,2,6]] C4-Helix code, designed for the early fault-tolerant regime. Using Quantinuum Helios, a 98-qubit trapped-ion quantum processor, we experimentally demonstrate the principal components of this architecture: we perform repeated quantum error correction with an error of
4.6−2.6+6.2×10−5 per logical qubit per QEC cycle. We benchmark the complete Clifford group on the two logical qubits of a single codeblock under active error correction, obtaining an error of
2.8−1.6+1.0×10−4 per two-qubit logical Clifford. We further demonstrate a fault-tolerant chain-map interface between
C4-Helix and a distance-5 surface code, preparing a heterogeneous three-logical-qubit GHZ state with a fidelity lower bound of
99.925−0.245+0.068%. In each case, the encoded implementation outperforms its corresponding unencoded physical baseline without relying on postselection. Circuit-level simulations indicate that improvements in physical fidelity bring the same architecture into the
10−6-
10−8 logical-error regime targeted for early fault-tolerant computation. Together, these results establish
C4-Helix as a hardware-validated fault-tolerant architecture rather than a bare quantum memory.
Quantum information processing and information exchange in the world of quantum computing demands novel methods, strategies and techniques based on quantum gates. Due to the facts that quantum computing is becoming more powerful and there are impactful scientific developments that would make quantum computers practical, post-quantum cryptography would require novel methods. In this sense, the paper presents a new approach or tool to be used in ciphering and deciphering information using multi-qubit control gates. This technique would be beneficial in terms of transforming information to another form and rebuilding it through asymmetric methods by the help of previously developed multi-qubit quantum gates. The underlying methodology of the technique is based on unitary transformations which may be divided into two parts: ciphering and deciphering parts. Moreover, controlling target qubits in accordance with the control qubit was also benefited within the methodology. In this sense, multi-qubit control gates, derived from mathematical model of universal control gates, play important role. Post-quantum cryptographic methods and strategies would be improved through this kind of methodologies.