Uts.edu.au
Researchers at the University of Technology Sydney have found that mechanically twisting atomically thin layers of hexagonal boron nitride — and crucially, doing so repeatedly — gives scientists an on-demand handle on quantum light sources that prior materials could not offer. The work, published June 19 in Science Advances, achieved a tuning range of more than 30 nanometers, equivalent to roughly 100 millielectronvolts, surpassing what strain-based methods had previously achieved for the same class of materials.
The result matters because spectral inhomogeneity — the tendency for quantum emitters in any given batch to emit at slightly different wavelengths rather than in lockstep — is the field’s primary engineering barrier to building scalable quantum photonic circuits. Photonic quantum computing requires multiple emitters to produce indistinguishable photons; without a post-fabrication way to bring those emitters into spectral alignment, each device must effectively be engineered from scratch. Twist-angle tuning offers, for the first time in hexagonal boron nitride, a reconfigurable correction mechanism that operates after the material has been assembled.
Quantum Emitters: Tiny Light Sources With a Control Problem
Quantum emitters are atomic-scale defects, or color centers, within a crystal lattice that emit single photons when electrically or optically excited. They are essential building blocks for quantum computing, quantum key distribution, and quantum sensing, because single photons are the currency of quantum information: they carry qubits over distance, connect nodes in quantum networks, and enable measurements beyond the classical noise floor.
The problem is control. In conventional solid-state hosts — diamond and silicon carbide being the most studied — quantum emitters are embedded in rigid, monolithic crystals. Once a device is fabricated at a particular geometry, its emitter properties are locked in. A researcher who needs different emission characteristics has essentially two options: accept the variability, or build an entirely new device.
“You can measure these quantum emitters and see that they exist, but it’s hard to make them work in practice,” said Dr. Angus Gale, the paper’s lead author. “This gives us a lever to get closer to that — a step towards the realization of quantum technologies.”
Why Hexagonal Boron Nitride Opens a Different Door
Hexagonal boron nitride is not a monolithic crystal in the conventional sense. It is a van der Waals material — a stack of two-dimensional atomic sheets held together by weak interlayer forces, rather than by the strong covalent or ionic bonds that lock conventional crystals together. The individual sheets can be mechanically exfoliated, repositioned, and restacked without fracturing the material.
That structural property is the key to the team’s approach. When the top hexagonal boron nitride layer is rotated relative to the layers below, the local stacking registry around each embedded defect changes — altering the crystal symmetry that the defect experiences and therefore shifting the energy levels of the photons it emits. Density functional theory calculations, which the team ran before conducting experiments, confirmed a strong dependence of emitter energy levels on both twist angle and the precise stacking configuration of the top layer. The experiments validated those predictions.
“We’re leveraging the fact that this material is layered,” said Gale. “We can pick it up, stack it, twist it, and use that twist to modify the emitters. You can’t really do that with traditional materials like diamond or silicon carbide.”
His analogy for a non-specialist audience: think of hexagonal boron nitride not as a block of cheese but as individual slices. A solid block gives you no access to the interior. With slices, you can peel layers apart, rearrange them, and change how they interact — then reassemble the whole differently whenever needed.
Why Spectral Tuning Unlocks Scalable Quantum Hardware
The 100 meV tuning range the team achieved is not just a number — it addresses a specific, named problem. Prior strain-based tuning of hexagonal boron nitride quantum emitters had reached roughly 65 meV in earlier work, and most other approaches offered significantly less. More importantly, those methods were static: once a strain configuration was set, the tuning was fixed.
What distinguishes the twist-angle approach is repeatability. The UTS team lifted, rotated, and restacked their hexagonal boron nitride layers multiple times over the course of the experiments, each time arriving at different emission wavelengths. This transforms twist angle from a one-time fabrication parameter into a continuous, adjustable degree of freedom — one that can in principle be set after a device is assembled and readjusted if the device’s requirements change.
For quantum photonic computing, this has direct implications. Multi-emitter entanglement operations require photons from different sources to be spectrally indistinguishable. Twist-angle tuning provides, for the first time in hexagonal boron nitride, a post-assembly mechanism to bring disparate emitters into spectral alignment without redesigning the underlying material.
“The benefit is that we used this twistable platform to shift the emission by a very significant amount,” said Gale. “Often when you control these systems, the amount of manipulation is very limited, but in this case the shift was much larger than expected.”
Twistronics Expands Into Quantum Photonics
The result also connects hexagonal boron nitride quantum emitters to the broader field of twistronics — the study of how stacking 2D materials at different angles creates moiré superlattices with properties neither individual layer possesses. The field drew widespread attention following the 2018 discovery that bilayer graphene, twisted to approximately 1.1 degrees, becomes superconducting.
That prior work, and subsequent results in transition metal dichalcogenides, established twist angle as a tunable parameter for electronic and magnetic properties. The UTS paper extends this toolkit into optical quantum engineering: twist angle now acts as a tunable parameter for the light-emitting properties of individual quantum defects as well.
“You can take two layers that don’t do much on their own, put them together at a specific angle, and suddenly you have a completely different system,” said Prof. Igor Aharonovich, the paper’s supervising author. Aharonovich’s group at UTS was among the first to report single-photon emission from hexagonal boron nitride defects, in a 2016 paper in Nature Nanotechnology that established the material as a serious quantum photonics platform.
Engineering Limits Still Ahead
The result is a materials-level demonstration, not yet a deployable quantum device. Several engineering gaps remain between this experiment and reconfigurable quantum hardware.
Deterministic placement of emitters — putting them at precisely specified locations within the crystal lattice — remains an open challenge. Current techniques can localize emitters to approximately 250 nanometers, limited by nanofabrication process constraints. Scalable fabrication of large emitter arrays with predictable positions has been demonstrated in proof-of-concept form, but is not yet routine.
Coherence times for hexagonal boron nitride emitters currently reach approximately 2 microseconds, shorter than the coherence times available in diamond nitrogen-vacancy centers, which can exceed milliseconds. For applications requiring long entanglement operations, this gap matters.
Integration with photonic cavities — the resonators needed to enhance emission rates and couple photons efficiently into optical circuits — also remains an active research frontier. The UTS team’s twist-tuning approach does not by itself solve the cavity-coupling problem, though it reduces one of the preconditions for coupling: spectral alignment between emitter and cavity resonance.
Prof. Aharonovich pointed to a wide range of emerging quantum applications that the advance could eventually contribute to, including healthcare diagnostics that require ultra-sensitive quantum sensors, cybersecurity infrastructure that relies on quantum key distribution, and improved GPS positioning systems that exploit the extreme sensitivity of quantum sensing. The team also noted that the twist-degree-of-freedom applies to thicker van der Waals crystals as well, not just thin flakes — a consideration relevant to manufacturing scale.
The paper, co-authored by Angus Gale, Seungjun Lee, Seungmin Park, Evan Williams, Helen Zhi Jie Zeng, James Liddle-Wesolowski, Young Duck Kim, Milos Toth, Tony Low, and Igor Aharonovich, was published in Science Advances on June 19, 2026.
Frequently Asked Questions
How do quantum emitters work?
Quantum emitters are atomic-scale defects — often called color centers — embedded in a crystal lattice. When excited by a laser pulse or electrical signal, they absorb energy, transition to a higher energy state, and then release that energy by emitting a single photon as they return to their ground state. Because the energy gap is fixed by the defect’s chemistry and local crystal environment, the emitter produces photons of a specific wavelength. This predictability makes them attractive as photon sources for quantum computing and quantum communication — but it also means that slight variations in the crystal environment cause different emitters to emit at slightly different wavelengths, a problem called spectral inhomogeneity that the UTS twist-tuning result directly addresses.
What is hexagonal boron nitride used for in quantum computing?
Hexagonal boron nitride hosts single-photon-emitting atomic defects that operate at room temperature — a significant advantage over many quantum emitter platforms that require cryogenic cooling. Its layered, van der Waals structure makes it mechanically manipulable in ways that diamond and silicon carbide are not, allowing researchers to tune emitter properties by twisting, stacking, or applying strain to the layers. It is also being explored as a low-loss dielectric for superconducting quantum circuits and as a platform for integrated quantum photonics, where its compatibility with on-chip waveguides and cavities is a key asset.
What are the biggest challenges in building quantum photonic hardware?
Three engineering barriers dominate the field. First, spectral inhomogeneity: individual quantum emitters in a given material emit at slightly different wavelengths, making it difficult to produce the indistinguishable photons that multi-qubit quantum operations require. Second, deterministic emitter placement: putting quantum emitters at precise locations within a chip-scale device is technically demanding and not yet routine at scale. Third, cavity integration: coupling emitters efficiently to optical cavities, which are needed to enhance emission rates and route photons into circuits, remains an open research challenge. The UTS twist-tuning result addresses the first challenge directly, and reduces one barrier to the third by enabling spectral alignment between an emitter and its target cavity resonance.