The challenge of achieving perfect randomness is deceptively subtle. In everyday life, we often take randomness for granted, assuming that flipping a coin or rolling a die yields outcomes that are equally likely. However, minute asymmetries in physical systems introduce subtle biases. Even the most carefully manufactured dice or coins succumb to physical imperfections that influence outcomes ever so slightly. In the realm of digital random number generation, especially those based on classical physical phenomena, similar biases persist, undermining attempts to generate flawless unpredictability. While these imperfections are negligible for most applications, they pose severe risks in cryptographic contexts where even minuscule deviations can be exploited by adversaries.

ETH Zurich’s breakthrough hinges on leveraging the intrinsic indeterminacy inherent in quantum systems. Unlike classical processes, quantum mechanics allows for outcomes that are fundamentally probabilistic, not merely unknown but genuinely random. Yet, even quantum random number generators—often reliant on phenomena like photon behavior at beam splitters—fail to deliver absolute perfection due to technical imperfections and environmental interference. To circumvent this, Renner and Wallraff’s teams devised an ingenious method called randomness amplification, which effectively purifies imperfect randomness into ideal, unassailable unpredictability.

The cornerstone of their approach is an enhanced Bell test, an experimental paradigm traditionally used to reveal entanglement, a uniquely quantum form of correlation defying classical explanation. By executing a rigorously optimized Bell test that achieves simultaneous high fidelity and rapid data throughput, they created an environment where the measurement outcomes displayed qualities unattainable by classical systems. Central to this setup are two superconducting quantum chips, each containing a quantum bit—or qubit—cooled to near absolute zero temperatures to minimize thermal noise and decoherence effects.

These two qubits are separated by an impressive 30 meters, linked by a tightly controlled cryogenic microwave channel. This spatial separation is crucial; it ensures that, during the measurement process, no information can travel between them fast enough—even at light speed—to influence results. This enforcement of the no-communication constraint safeguards against local hidden variable explanations that could otherwise simulate randomness in classical physics. When one qubit is measured, the outcome inherently and instantaneously affects the state of the other due to entanglement, yet the randomness of these results remains inviolate and certifiable.

What sets this experiment apart is the innovative way measurement settings on the qubits were chosen based on a previously imperfect random number generator. By feeding these “weak” random inputs into the system and then applying sophisticated post-processing algorithms developed by Renner’s theoretical team, the output sequence was rigorously tested and verified to be free of any discernible pattern or bias. This two-step process—amplification via quantum measurement followed by algorithmic refinement—culminated in randomness that is, for all practical and theoretical purposes, perfect.

Renner underscores the significance of this accomplishment by comparing it to crossing a formidable threshold: “Our technical advancements have enabled us to produce random numbers that will remain perfectly random for eternity regardless of any future analytical techniques applied.” This certifiable randomness endows the output with a degree of security and reliability previously unattainable, establishing a new gold standard in random number generation.

Beyond its theoretical elegance, the real-world implications of this research are profound. Certified, unassailable randomness is the cornerstone of secure communication protocols, digital identity verification, and robust encryption systems. Much like atomic clocks revolutionized timekeeping by offering precise, universally accepted standards, this quantum randomness amplifier has the potential to become the definitive source of randomness, indispensable in a world increasingly reliant on digital security.

Particularly in the emerging landscape of quantum-safe cryptography, where classical methods will soon be threatened by advances in quantum computing, ensuring the unpredictability of cryptographic keys is paramount. The strength of any encryption scheme inherently depends on the quality of its random components; weak randomness translates to vulnerabilities, jeopardizing entire systems. ETH Zurich’s method offers a physical guarantee against such weaknesses, empowering next-generation security architectures.

Moreover, this protocol could underpin public randomness services vital for fair lotteries, blockchain consensus mechanisms, and complex simulations requiring unbiased random inputs. Traditionally, these domains have struggled with ensuring unpredictability, but the application of quantum-verified randomness transforms the landscape, imbuing processes with scientific legitimacy and trustworthiness.

Technically, the filtering of imperfections in quantum randomness relies on meticulous control and measurement precision. The superconducting qubits enable extended coherence times and controllable interactions through microwave photons, while the ultra-low temperatures suppress decoherence and noise. The careful synchronization and spatial separation of qubits uphold the stringent conditions necessary for loophole-free Bell tests. These refined experimental capabilities have matured only recently, underscoring the interplay of cutting-edge materials science, cryogenics, and quantum information theory inherent in this accomplishment.

As the community digests these findings, the ETH Zurich team’s work stands not merely as an experimental tour de force but as a harbinger of a new era. An era where quantum physics is not just a theoretical curiosity but a practical resource enabling technologies that safeguard information in fundamentally unprecedented ways. The age of perfectly random numbers is now no longer an abstract possibility but a tangible reality.

This research underscores the relentless march of quantum technologies from laboratory curiosity toward indispensable infrastructure. It exemplifies how deep theoretical insights, married to experimental innovation, can surmount challenges deemed insurmountable. By turning imperfect randomness into an infinite wellspring of genuine unpredictability, ETH Zurich’s quantum-enhanced randomness amplifier reshapes the foundations of digital trust and security for the decades to come.

Subject of Research: Quantum Randomness Amplification

Article Title: Experimental Randomness Amplification

News Publication Date: 1-Apr-2026

Web References: DOI: 10.1038/s41586-026-10521-8

Image Credits: Kilian Kessler / ETH Zurich

Keywords

Quantum Physics, Randomness Amplification, Quantum Random Number Generator, Bell Test, Quantum Entanglement, Superconducting Qubits, Cryptography, Quantum Security, Quantum Computing, Digital Encryption, Quantum Measurement, Certified Randomness

To mitigate such errors, the concept of logical qubits—constructed from ensembles of multiple physical qubits—has become central. By deploying continuous error correction protocols, these logical qubits maintain quantum information integrity over time despite pervasive noise. Nonetheless, the technology must transcend mere data preservation and facilitate quantum gate operations, the fundamental building blocks for quantum algorithms, while actively correcting errors as computations unfold.

A groundbreaking experimental leap has been achieved by the team led by Professor Andreas Wallraff at ETH Zurich, in collaboration with researchers from the Paul Scherrer Institute and theoretical physicists at RWTH Aachen University and Forschungszentrum Jülich. Their study, recently published in Nature Physics, demonstrates a pioneering approach to performing quantum logical operations on superconducting qubits with concurrent error correction—a feat that addresses a critical bottleneck in realizing functional quantum processors.

Quantum error correction diverges starkly from its classical counterpart. Classical error correction relies on creating multiple identical copies of bits and employing majority voting to detect and rectify bit flips. Such cloning techniques, however, are infeasible in quantum mechanics due to the no-cloning theorem. Instead, quantum information is safeguarded by encoding it into entangled states distributed across many physical qubits. This entanglement-based framework must also correct phase-flip errors, unique to quantum computation, alongside bit flips, exponentially complicating error management.

Surface codes have emerged as one of the most promising architectures for quantum error correction. In this scheme, a logical qubit’s state is embedded within many physical ‘data qubits.’ Error correction hinges on the measurement of ‘stabilizers’—special qubits linked to data qubits designed to detect deviations in bit and phase values without collapsing the stored quantum information. Specifically, Z-type stabilizers signal bit-flip errors, while X-type stabilizers detect phase flips. The data qubits themselves remain unmeasured and hence preserve the encoded logical state.

Crucially, executing logical operations such as the controlled-NOT gate between two logical qubits requires even more nuanced control since errors can manifest during the gate operation itself. Ideally, qubits would be spatially movable, allowing arbitrary interactions. Yet, in superconducting qubit arrays arranged on fixed two-dimensional lattices, connectivity is constrained by physical proximity—only adjacent qubits can interact directly. This spatial limitation necessitates inventive strategies to perform fault-tolerant logical gates.

The breakthrough comes through the realization of ‘lattice surgery,’ a method that reconciles these spatial constraints. In their experiment, the researchers encoded a single logical qubit using 17 physical qubits arranged roughly in a square lattice. By cyclically reading the stabilizers every 1.66 microseconds, they implemented ongoing correction of both bit-flip and phase-flip errors, ensuring robust logical qubit stability.

When time progressed to performing the operation termed ‘surgery,’ the team selectively read out three data qubits centered in the square, effectively splitting the surface code into two distinct halves. Concurrently, they suspended the measurement of X-type stabilizers. This deft manipulation produced two logically entangled qubits—an essential stepping stone towards complex quantum gate operations. Throughout this lattice surgery, bit-flip errors were continuously corrected and subsequently the error correction process resumed independently on both resulting halves.

While this initial lattice surgery operation is not a complete controlled-NOT gate, it forms the foundational building block for such gates. Through a sequence of lattice surgery splits and merges, it becomes possible to compose the full range of fault-tolerant quantum logic operations. Researcher Michael Kerschbaum elucidates that performing such logical operations fault-tolerantly under fixed spatial constraints would be straightforward if qubit repositioning were possible; lattice surgery ingeniously bypasses this limit.

This demonstration constitutes the first realization of lattice surgery on superconducting qubits—a milestone that significantly advances the field’s pursuit of scalable, error-resilient quantum computing. Nevertheless, challenges remain: to fully stabilize the splitting operation against phase-flip errors, the system would require scaling to at least 41 physical qubits per logical qubit. Despite these hurdles, this achievement demonstrates the feasibility of complex logical manipulations in current hardware platforms.

The implications of incorporating lattice surgery into superconducting qubit architectures are profound. By enabling fault-tolerant logical gates within the physical constraints of planar qubit arrays, this technique paves a crucial path toward quantum devices composed of thousands, or even millions, of qubits. These larger quantum processors could handle significantly more intricate algorithms and error rates, bringing practical quantum computing closer than ever before.

Furthermore, the ability to perform quantum operations while dynamically correcting errors heralds a new era in quantum control precision and architectural design. The meticulous interplay of stabilizer measurements, selective readouts, and lattice surgery processes highlights how intricate quantum engineering must be to actualize reliable information processing beyond classical limits.

In summary, the Wallraff team’s experimental success at ETH Zurich and their collaborators represents a landmark step in the ongoing quest for usable quantum computers. Their lattice surgery approach cleverly navigates the spatial limitations inherent in superconducting qubits, effectively balancing quantum coherence and fault tolerance. As the technology matures and qubit numbers grow, such innovations will underpin the quantum revolution poised to transform computation, simulation, and encryption paradigms worldwide.

Subject of Research: Quantum error correction and fault-tolerant quantum operations in superconducting qubits

Article Title: Realizing lattice surgery on two distance-three repetition codes with superconducting qubits

News Publication Date: 30-Jan-2026

Web References:
DOI:10.1038/s41567-025-03090-6
Press release by Forschungszentrum Jülich (in German)

References:
Besedin, I., Kerschbaum, M. et al. Realizing lattice surgery on two distance-three repetition codes with superconducting qubits. Nat. Phys. (2026).

Image Credits: Quantum Device Lab / ETH Zurich

Keywords

Quantum computing, error correction, superconducting qubits, logical qubits, lattice surgery, surface codes, fault-tolerant quantum gates, bit-flip errors, phase-flip errors, quantum algorithms, quantum entanglement, quantum decoherence