Enhancing Quantum Computing: Overcoming Connectivity Limitations in Superconducting Devices

Quantum computers have the potential to revolutionize society by solving complex problems that classical computers cannot. However, their performance is limited by uncontrollable noise and errors. Recent progress in noisy intermediate-scale quantum (NISQ) devices offers new opportunities for many-body physics. This research focuses on superconducting quantum processors, which are easy to fabricate and versatile. However, their performance is limited by noise and decoherence. The researchers have found that long-range interactions can improve the performance of quantum hardware. They have also overcome the limitations of qubit connectivity in NISQ devices, opening up new possibilities for the simulation of complex quantum many-body systems.

What is the Potential of Quantum Computers, and How Can They Be Improved?

Quantum computers are a revolutionary technology with the potential to transform society by solving problems that classical computers cannot. However, these machines are still subject to uncontrollable noise and errors that limit their performance. Despite these limitations, recent progress in noisy intermediate-scale quantum (NISQ) devices represents an exciting opportunity for many-body physics by introducing new laboratory platforms with unprecedented control and measurement capabilities.

Quantum simulation of the dynamics of increasingly complex quantum many-body systems is expected to be one of the most promising short-term goals of NISQ quantum computing devices. These simulations have intriguing applications in diverse areas ranging from quantum chemistry and material science to high-energy physics.

Various experimental platforms have been tested for quantum computing, including trapped ions, neutral Rydberg atoms, coherent photons, nuclear spins in molecules, nitrogen-vacancy (NV) centers, and superconducting qubits. Each platform has its own advantages and drawbacks.

Why are Superconducting Quantum Processors Important?

In this research, the focus is on superconducting quantum processors. Superconducting qubits are relatively easy to fabricate and can be densely packed, allowing for the construction of large-scale quantum computers. This makes them a promising platform for scaling up quantum computing applications.

Moreover, superconducting qubits can be manipulated with various microwave frequencies, making them versatile and flexible for implementing various quantum gates. Thanks to this flexibility, the number of quantum simulations implemented on noisy superconducting devices has steadily risen in recent years.

However, the performance of superconducting NISQ devices is limited by the presence of various sources of noise and decoherence, whose impact grows with the depth and complexity of the quantum circuit realized. This limits the investigation of non-local effects and complex geometries.

How Can Long-Range Interactions Improve Quantum Hardware?

Long-range interactions are known to boost the performance of quantum hardware, as they evade the traditional constraint imposed by thermal equilibration and noise propagation. The stability of long-range quantum systems against external perturbations and their role as a source of unprecedented phenomena, including novel forms of dynamical phase transitions and defect formation, anomalous thermalization and information spreading metastable phases, and entanglement scalings, have been widely proven.

However, the theoretical comprehension of such behaviors is still mainly limited to integrable quadratic systems or perturbations of fully connected mean-field models. In contrast, systems with a tunable interaction range require an extremely high degree of experimental control.

What is the Main Limitation of Superconducting NISQ Devices?

One main limitation of superconducting NISQ devices is their minimal connectivity. Superconducting qubits are typically arranged in a one or two-dimensional grid with nearest-neighbor connectivity, making it challenging to implement quantum algorithms that require long-range interactions.

In this research, the scientists present the outcomes of a digital quantum simulation where they overcome the limitations of the qubit connectivity in NISQ devices. Utilizing the universality of quantum processor native gates, they demonstrate how to implement couplings among physically disconnected qubits at the cost of increasing the circuit depth.

What is the Significance of This Research?

This research addresses one of the significant limitations of superconducting quantum processors: device connectivity. It reveals that non-trivial physics involving couplings beyond nearest neighbors can be extracted after the noise impact is properly considered in the theoretical model and consequently mitigated from the experimental data.

The researchers applied this method to simulate a Floquet-driven quantum spin-chain featuring interactions beyond nearest neighbors. Specifically, they benchmarked the prethermal stabilization of the discrete Floquet time-crystalline response as the interaction range increases, a phenomenon never observed experimentally before.

This research opens up new possibilities for simulating complex quantum many-body systems, a promising short-term goal of NISQ devices. It also provides valuable insights into the potential of superconducting quantum processors and how their performance can be improved.