How big quantum computers could keep their qubits under control

Irfan A. Siddiqi

Thomas Bækkegaard, Lasse Bjørn Kristensen, Niels Jakob Søe Loft +3 more

As classical computers struggle to keep up with Moore's law, quantum computing may represent a big step in technology and yield significant improvement over classical computing for many important tasks. Building a quantum computer, however, is a daunting challenge since it requires good control but also good isolation from the environment to minimize decoherence. It is therefore important to realize quantum gates efficiently, using as few operations as possible, to reduce the amount of required control and operation time and thus improve the quantum state coherence. Here we propose a superconducting circuit for implementing a tunable spin chain consisting of a qutrit (three-level system analogous to spin-1) coupled to two qubits (spin-1/2). Our system can efficiently accomplish various quantum information tasks, including generation of entanglement of the two qubits and conditional three-qubit quantum gates, such as the Toffoli and Fredkin gates, which are universal for reversible classical computations. Furthermore, our system realizes a conditional geometric gate which may be used for holonomic (non-adiabatic) quantum computing. The efficiency, robustness and universality of our circuit makes it a promising candidate to serve as a building block for larger spin networks capable of performing involved quantum computational tasks.

Kamil A. Valiev

Mehrdad Zarei, Ivo H. A. Knottnerus, Alexander Urech +3 more

One of the key technologies in cold atom experiments such as optical atomic clocks, quantum computers and simulators, as well as in optical communication and time keeping, is taking advantage of the external-cavity diode lasers (ECDLs). Because of the high sophistication of cold atom experiments, it is very important to have full control over frequency and single mode operation of the laser. Fully automatic control in cold atom experiments, including relocking lasers' stabilization, frequency control of repumping lasers, control over currents in magnetic field coils [1] is a big challenge. On the other hand, it is crucial in high-TRL cold atom applications, such as transportable optical clocks [2]–[4], and quantum computers [5].

Dheeraj Sai Tukkugudam

Quantum networking is causing a revolution in technology. It allows secure communication and spreads quantum computing through interactions based on entanglement. However, keeping qubit coherence and making sure transmission is high-quality are big problems. This is because of decoherence, the times spent waiting for entanglement, and the delays in synchronizing up. This study suggests an improved quantum memory system to tackle these issues. It does this through making entanglement in parallel using reinforcement learning to schedule jobs and advanced ways to stop decoherence. These include quantum error correction (QEC) and dynamic decoupling (DD). The study creates a math formula to make fidelity as good as possible. It shows that this problem can be solved in polynomial time. Tests show that this system improves how well fidelity is kept and how well quantum states are sent overall. This proves that the suggested system is a good way to create quantum networks that can grow and be trusted.

Simon J. Devitt