Q

© Springer Nature Switzerland AG 2018. This paper describes a quantum programming environment, named Q| SI⟩, to support quantum programming using a quantum extension of the while -language. Embedded in the.Net framework, the Q| SI⟩ platform includes a quantum while -language compiler and a suite of tools to simulate quantum computation, optimize quantum circuits, analyze and verify quantum programs. This paper demonstrates Q| SI⟩ in use. Quantum behaviors are simulated on classical platforms with a combination of components and the compilation procedures for different back-ends are described in detail. Q| SI⟩ bridges the gap between quantum hardware and software. As a scalable framework, this platform allows users to code and simulate customized functions, optimize them for a range of quantum circuits, analyze the termination of a quantum program, and verify the program’s correctness (The software of Q| SI⟩ is available at http://www.qcompiler.com.)

Spin qubits in graphene quantum dots

The main characteristics of good qubits are long coherence times in combination with fast operating times. It is well known that carbon-based materials could increase the coherence times of spin qubits, which are among the most developed solid-state qubits. Here, we propose how to form spin qubits in graphene quantum dots. A crucial requirement to achieve this goal is to find quantum-dot states where the usual valley degeneracy in bulk graphene is lifted. We show that this problem can be avoided in quantum dots based on ribbons of graphene with armchair boundaries. The most remarkable new feature of the proposed spin qubits is that, in an array of many qubits, it is possible to couple any two of them via Heisenberg exchange with the others being decoupled by detuning. This unique feature is a direct consequence of the quasi-relativistic spectrum of graphene