AsianScientist (Jan. 8, 2019) – An international team of researchers has crafted a new architecture for quantum computing using two different types of quantum bits, or qubits. They published their findings in the journal Nature Communications.
Quantum computers, which rely on qubits to perform complex calculations, have the potential to tackle difficult mathematical problems that cannot be solved using ordinary computers. However, for scalable quantum computing to occur, a quantum device must first be initialized quickly, which means that the qubits must be rapidly induced to take on a certain spin state.
Secondly, the quantum computer must maintain coherence for a time long enough to make a measurement. Coherence refers to the entanglement between two quantum states, and ultimately this is used to make the measurement. If qubits become decoherent due to environmental noise, for example, the device becomes worthless. Finally, the ultimate state of the qubit must be read out quickly.
To achieve scalable quantum computing, an international group of researchers led by the RIKEN Center for Emergent Matter Science, Japan, have constructed a hybrid device that makes use of two different types of qubits for computation.
The first type of single-spin qubit, called a Loss-DiVincenzo qubit, has very high control fidelity, meaning that it is in a well-defined state, making it ideal for calculations. The Loss-DiVincenzo qubit also has a long decoherence time, so it stays in a given state for a relatively long time before losing its signal to the environment. Unfortunately, the downside to these qubits is that they cannot be quickly initialized into a state or read out.
Hence, a second type of qubit—called a singlet-triplet qubit—becomes necessary. Unlike the Loss-DiVincenzo qubit, the singlet-triplet qubit is quickly initialized and read out, but it rapidly becomes decoherent. For the study, the scientists combined the two types of qubits with a type of quantum gate known as a controlled phase gate, which allowed spin states to be entangled between the qubits in a time fast enough to maintain coherence. Hence, the state of the Loss-DiVincenzo qubit could be read out by making measurements of the fast singlet-triplet qubit.
“With this study we have demonstrated that different types of quantum dots can be combined on a single device to overcome their respective limitations. This offers important insights that can contribute to the scalability of quantum computers,” said Dr. Akito Noiri of RIKEN, the lead author of the study,
The article can be found at: Noiri et al. (2018) A Fast Quantum Interface Between Different Spin Qubit Encodings.
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Source: RIKEN; Photo: Shutterstock.
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