IQM Star is a superconducting quantum processor topology that connects multiple qubits through a central computational resonator. While this topology is available already, IQM has just published exciting results in three new research papers on this topology. These papers outline that IQM Star has the potential to scale and solve issues like how we can more efficiently correct errors on quantum algorithm results to create quantum computers that outperform classical ones.  

If you are interested in the nitty-gritty technical facts and detailed results, you can jump into the papers here:  

1. A Superconducting Qubit-Resonator Quantum Processor with Effective All-to-All Connectivity 
2. Quantum Error Detection in Qubit-Resonator IQM Star Architecture 
3. Quantum Algorithms for Simulating Systems Coupled to Bosonic Modes Using a Hybrid Resonator-Qubit Quantum Computer

This blog will give you an overview of what IQM Star is, how it compares to traditional grid or lattice architectures, and what the benefits of this new topology are.

 

The Need for a New Approach: Addressing the Limitations of Traditional Quantum Processors 

Most quantum processors today use square (grid/lattice) topologies, where qubits are arranged in a structured, often 2D, pattern.  

This topology is the most common one for superconducting qubits, because it’s relatively easy to manufacture, it’s well-researched, and it’s easily scalable. IQM’s Crystal is a great example of a high-fidelity QPU in this style. But while this setup suits many needs, it does have its limits: 

• Lower connectivity: Qubits can only interact with their immediate neighbors, requiring extra gate operations (like SWAP gates) to enable interactions between distant qubits. 

• Noisy SWAP networks: These gates reduce circuit fidelity. This, in turn, can negatively impact the accuracy of the quantum algorithm’s results. 

• Restricted error correction: Lattice topologies work great with a method of error correction called surface codes. Other error correction options, like color codes and qLDPC codes, show promise to outperform surface codes but they cannot be easily implemented for lattice QPUs.

And, while this is the topology of choice for most, it has not yet been successful in reaching quantum advantage. Time to start exploring off-the-grid. 

The IQM Star addresses a lot of these issues. It effectively connects all qubits through a resonator, which is rare in superconducting technology. This resonator acts as a computational element, enabling direct, high-fidelity interactions between all qubits.

 

A Departure from Tradition: How IQM Star Stands Apart 

1. Effective all-to-all connectivity: Any qubit can interact with any other qubit, eliminating the need for noisy SWAP gates.
   
2. Improved error resilience: The shared resonator allows for more efficient quantum error detection and correction.
3. Efficient quantum algorithm execution: Algorithms that require high qubit connectivity, such as quantum simulations and variational quantum eigensolvers (VQEs), can run more efficiently.

IQM Star vs. Traditional Lattice-Based Quantum Processor Architectures 

How does the IQM Star QPU compare to conventional square/lattice architectures? 

Feature	Traditional Lattice QPU	IQM Star QPU Topology
Qubit Connectivity	Limited (nearest neighbors)	All-to-all (via resonator)
Need for SWAP Gates	High (adds noise)	Low (direct interactions)
Error Correction	Works best with surface codes	Compatible with novel QEC codes, like color codes & qLDPC codes
Algorithm runtime	Slower due to restricted connectivity	Faster for highly connected algorithms

 

IQM Star for Simulating Complex Quantum Systems 

The high connectivity and computational resonator of the IQM Star QPU make it ideal for several advanced quantum applications: 

• The resonator itself participates in computations. This is particularly effective for simulating bosonic modes, which appear in quantum chemistry, material science, and condensed matter physics.

Quantum Error Correction and Fault-Tolerant Computing 

• IQM Star effective all-to-all connectivity enables new quantum error detection codes, such as color codes and quantum LDPC (Low-Density Parity Check) codes, which have the potential to outperform traditional surface codes. 

• IQM Star’s performance has been tested using an error detection algorithm to encode two logical qubits and obtained logical state fidelities exceeding 96% and logical error per cycle below 1%, which makes this design promising for scalable quantum computing.

High-Connectivity Quantum Algorithms

• Apart from the overall reduction of two-qubit gates, the high connectivity of IQM Star is particularly useful for problems that can be solved by the so-called quantum approximate optimization algorithm.  

• The capability of a quantum device to run such an algorithm is measured by the Q-Score benchmark. For this QPU, we’ve measured a particularly high Q-Score of 6+1, which demonstrates the benefit of an effective all-to-all qubit connectivity.

What Makes IQM Star Revolutionary: The Results 

IQM Star isn’t just a minor tweak to existing designs, it introduces game-changing concepts in quantum processing: 

Resonator as a Computational Element 

• Unlike traditional architectures where resonators are only used for qubit readout, the IQM Star QPU actively uses the resonator in computation. 
• This unlocks new quantum algorithms that leverage resonator-mediated interactions for faster processing.

Error Mitigation 

• The system is fully compatible with advanced error mitigation techniques, including noise-robust estimation (NRE) and zero-noise extrapolation (ZNE). 
• Experiments show that NRE can recover noise-free quantum measurements with >96% accuracy (logical fidelity from 96.6% to 99.9% for all characterized logical states).

Achieving High-Fidelity Quantum States 

• The IQM Star QPU successfully demonstrated the creation of high-fidelity GHZ states on 6 qubits with an error-mitigated fidelity of 0.86. 
• This result is promising for applications that require large-scale quantum entanglement.

What’s Next? 

The landscape of quantum computing is shifting, and with it, new opportunities are emerging. IQM Star opens doors to quantum architectures that have the potential to be more adaptable, more scalable, and better suited to real-world applications. 

We are just getting started, and IQM Star’s potential future applications are even more exciting: 

Quantum Hardware-Efficient Error Correction 

• The ability to support qubit-count efficient QEC codes could lead to faster development of fault-tolerant quantum computing.

Advancements in Quantum Machine Learning 

• The IQM Star topology could power quantum neural networks (QNNs) with efficient, high-connectivity architectures.

Expanding the Role of Resonators in Computation 

• Future research could enhance the role of resonators, allowing for more powerful quantum hybrid systems that integrate bosonic computing.