Decoherence Impact on Flying Qubits: A Step Forward in Quantum Computing

Researchers from the Université Grenoble Alpes, Chapman University, and the National University of Singapore have studied the impact of decoherence on flying qubits, a significant issue in quantum computing. They found that decoherence, which causes quantum systems to behave more like classical systems, can significantly affect ballistic qubits. The team proposed a method to counteract this decoherence, which could improve the performance and reliability of quantum systems. This research not only has implications for quantum computing but also contributes to the fundamental understanding of quantum systems, including quantum optics and quantum thermodynamics.

What is the Impact of Decoherence on Flying Qubits?

Decoherence is a phenomenon that affects quantum systems, causing them to lose their quantum properties and behave more like classical systems. This is a significant issue in the field of quantum computing, where the power of these systems lies in their ability to maintain quantum states. In a recent study by researchers from various institutions, including the Université Grenoble Alpes, Chapman University, and the National University of Singapore, the impact of decoherence on flying qubits was examined.

The researchers implemented an effective time-dependent Hamiltonian by making a quantum system fly through an inhomogeneous potential. This process, for instance, realizes a quantum gate on its internal degrees of freedom. However, flying systems have a spatial spread that will generically entangle the internal and spatial degrees of freedom, leading to decoherence in the internal state dynamics, even in the absence of any external reservoir.

The team provided formulas valid at all times for the dynamics fidelity and change of entropy for small spatial spreads, quantified by x. This decoherence is non-Markovian, and its effect can be significant for ballistic qubits, scaling as x^2, but not for qubits carried by a moving potential well, scaling as x^6. They also proposed a method to completely counteract this decoherence for a ballistic qubit later measured.

How are Flying Quantum Systems Utilized?

Flying quantum systems, such as flying Rydberg atoms, flying spin qubits, or flying electrons, have both practical and fundamental significance. Practically, there is great hope to use the internal state of such flying quantum systems to process quantum information. This is a goal of recent experiments on flying electrons in solid-state devices, with quantum information carried by the electrons’ spins or its spatial distribution.

Similar ideas have long been applied to flying Rydberg atoms. Fundamentally, these systems are the simplest examples of how time-dependent Hamiltonians emerge from time-independent ones, i.e., how non-autonomous dynamics emerge from autonomous ones. This concept is used in various areas of quantum physics, including measurement paradoxes, quantum optics, quantum collision models, and quantum thermodynamics.

The researchers illustrated this with a ballistic quantum system moving at constant velocity to enter and exit from an interaction region acting on its internal state. This interaction region is a key component of the system, as it is where the quantum system interacts with the potential, leading to changes in its internal state.

What are the Implications of this Research?

The research conducted by the team has significant implications for the field of quantum computing. By understanding the impact of decoherence on flying qubits, strategies can be developed to mitigate this effect and maintain the quantum properties of these systems. This is crucial for the development of quantum computers, which rely on the maintenance of quantum states to perform complex calculations at speeds far exceeding those of classical computers.

The researchers’ work also contributes to the fundamental understanding of quantum systems. By examining how time-dependent Hamiltonians emerge from time-independent ones, they shed light on the nature of non-autonomous dynamics in quantum systems. This understanding is not only important for the development of quantum computers but also for other areas of quantum physics, including quantum optics and quantum thermodynamics.

Finally, the researchers’ proposal of a method to counteract decoherence in ballistic qubits could have practical applications in the design of quantum systems. By implementing this method, it may be possible to create quantum systems that are more resistant to decoherence, thereby improving their performance and reliability. This could be a significant step forward in the development of practical quantum computing systems.