Russian Researchers Explore Stability of Qubits in Quantum Computing

Researchers from Samara National Research University have explored the dynamics of two and three identical qubits interacting with a common thermal field of a lossless resonator. The study found that an increase in the average number of photons in the mode leads to a decrease in the maximum degree of entanglement. It also revealed that a two-qubit entangled state is more stable against external noise than three-qubit entangled states. The research is significant as entangled states are the main resource of quantum physics for quantum computing, communications, cryptography, and metrology. Future research will focus on preventing the instantaneous death of entanglement of qubits caused by interaction with thermal fields of resonators.

What is the Dynamics of Entangled States in a Three-Qubit Thermal Model?

In a recent scientific article, researchers Alexander Bagrov and Evgeny Bashkirov from Samara National Research University in Russia have explored the dynamics of two and three identical qubits resonantly interacting with a selected mode of a common thermal field of a lossless resonator. The researchers found a solution to the quantum temporal Liouville equation for various three and two-qubit entangled states of qubits.

The study focused on the calculation of the criterion of entanglement of qubits and the degree of coincidence. The results of numerical modeling of the degree of coincidence showed that an increase in the average number of photons in the mode leads to a decrease in the maximum degree of entanglement. It was also shown that a two-qubit entangled state is more stable against external noise than three-qubit entangled states of Greenberger-Horne-Zeilinger (GHZ). Furthermore, a truly entangled GHZ state is more resistant to noise than a GHZ-like entangled state.

What are the Key Concepts in the Study?

The key concepts in the study include qubits, three-qubit states of Greenberger-Horne-Zeilinger, resonant interaction, resonator, thermal field, entanglement, and degree of coincidence. Qubits, or quantum bits, are the fundamental units of quantum information. They are quantum systems with two states, similar to the binary states of classical bits, but with the added ability to exist in a superposition of states.

The Greenberger-Horne-Zeilinger (GHZ) state is a specific type of entangled quantum state that involves three or more qubits. It is named after the physicists who first proposed its existence. The GHZ state is particularly interesting because it exhibits a stronger form of quantum entanglement known as “non-local” entanglement, where the state of each qubit is immediately connected to the state of the other qubits, regardless of the distance between them.

What is the Significance of the Research?

Entangled states are currently the main resource of quantum physics for quantum computing, quantum communications, quantum cryptography, and quantum metrology. Using different classes of entangled states can accelerate calculations, ensure communication security, and overcome standard quantum limits in measurements.

For multi-qubit systems, there are several non-equivalent classes of entangled states. In particular, for the simplest case of a three-qubit system, there are only two genuinely entangled states. These include the entangled states of Greenberger-Horne-Zeilinger (GHZ states) and the entangled states of Werner (W-states). Among all classes of entangled states, GHZ states are one of the most demanded states for the purposes of quantum informatics and quantum metrology.

What are the Challenges and Opportunities in the Field?

The accuracy and technical complexities in implementing entangled states of qubits grow exponentially with the increase in the number of qubits. The difficulties of theoretical analysis of the dynamics of GHZ states also significantly increase with the increase in the number of qubits in the system. Therefore, special attention is paid to the analysis of three-qubit systems in theoretical considerations.

In recent years, multi-particle GHZ states have been implemented for various physical systems of qubits, ions in traps, Rydberg atoms, photons, and superconducting qubits. These works have opened new opportunities in the development of scalable quantum computers, quantum metrology, and quantum communication.

What are the Future Directions of the Research?

The study of methods to prevent the effect of instantaneous death of entanglement of qubits caused by interaction with thermal fields of resonators is of significant interest. The study of this effect for qubits interacting with thermal noise of resonators is especially important because all quantum devices necessarily contain thermal photons in resonators.

In their work, Bagrov and Bashkirov thoroughly investigated the dynamics of entanglement in a system of three qubits resonantly interacting with the mode of a thermal quantum electromagnetic field in an ideal resonator for separable, bi-separable, and genuinely entangled states of the W-type. It was shown that the effect of instantaneous death of entanglement takes place for any intensities of the thermal field of the resonator. It is of great interest to study the dynamics of the three-qubit model in the resonator for a genuinely entangled state of qubits of the GHZ type.