**Quantum News Briefs September 27** opens with announcement that “Quantinuum Sets New Record with Highest Ever Quantum Volume”; followed by PsiQuantum’s goal to outperform every supercomputer with its million qubit photonic quantum computer. Third is Chalmers researchers reaching unprecedented control over captured light.

The three milestones, representing actionable acceleration for the quantum computing eco- system, are: (i) new arbitrary angle gate capabilities on the H-series hardware, (ii) another QV record for the System Model H1 hardware, and (iii) over 500,000 downloads of Quantinuum’s open-sourced TKET, a world-leading quantum software development kit (SDK)

“Quantinuum is accelerating quantum computing’s impact to the world,” Uttley said. “We are making significant progress with both our hardware and software, in addition to building a community of developers who are using our TKET SDK,” explains Uttley

This latest quantum volume measurement of 8192 is particularly noteworthy and is the second time this year Quantinuum has published a new QV record on their trapped-ion quantum computing platform, the System Model H1, Powered by Honeywell.

A key to achieving this latest record is the new capability of directly implementing arbitrary angle two-qubit gates. For many quantum circuits, this new way of doing a two-qubit gate allows for more efficient circuit construction and leads to higher fidelity results. This new gate design represents a third method for Quantinuum to improve the efficiency of the H1 generation, said Dr. Jenni Strabley, Senior Director of Offering Management at Quantinuum.

**A powerful new capability: More information on arbitrary angle gates **

Currently, researchers can do single qubit gates — rotations on a single qubit — or a fully entangling two-qubit gate. It’s possible to build any quantum operation out of just those building blocks. With arbitrary angle gates, instead of just having a two-qubit gate that’s fully entangling, scientists can use a two-qubit gate that is partially entangling.

This is a powerful new capability, particularly for noisy intermediate-scale quantum algorithms. Another demonstration from the Quantinuum team was to use arbitrary angle two-qubit gates to study non-equilibrium phase transitions, the technical details of which are available on the arXiv here.

**A new milestone in quantum volume**

This represents a new milestone in quantum volume which requires running arbitrary circuits. At each slice of the quantum volume circuit, the qubits are randomly paired up and a complex two-qubit operation is performed. This SU(4) gate can be constructed more efficiently using the arbitrary angle two-qubit gate, lowering the error at each step of the algorithm.

**Building a quantum ecosystem among developers**

Quantinuum has also achieved another milestone: over 500,000 downloads of TKET.

TKET is an advanced software development kit for writing and running programs on gate-based quantum computers. TKET enables developers to optimize their quantum algorithms, reducing the computational resources required, which is important in the NISQ era. Quantinuum CEO Ilyas Khan said, “Whilst we do not have the exact number of users of TKET, it is clear that we are growing towards a million people around the world who have taken advantage of a critical tool that integrates across multiple platforms and makes those platforms perform better. We continue to be thrilled by the way that TKET helps democratize as well as accelerate innovation in quantum computing.”

**Additional Data for Quantum Volume 8192**

The System Model H1-1 successfully passed the quantum volume 8192 benchmark, outputting heavy outcomes 69.33% of the time, with a 95% confidence interval lower bound of 68.38% which is above the 2/3 threshold.

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## PsiQuantum’s goal to outperform every supercomputer with its million qubit photonic quantum computer

Light is used for various operations in superconductors and atomic quantum computers. PsiQuantum also uses light and turns infinitesimally small photons of light into qubits. Of the two types of photonic qubits – squeezed light and single photons – PsiQuantum’s technology of choice is single-photon qubits.

Dr. Shadbolt explained that detecting a single photon from a light beam is analogous to collecting a single specified drop of water from the Amazon river’s volume at its widest point. “That process is occurring on a chip the size of a quarter,” Dr. Shadbolt said. “Extraordinary engineering and physics are happening inside PsiQuantum chips. We are constantly improving the chip’s fidelity and single photon source performance.”

When PsiQuantum announced its Series D funding a year ago, the company revealed it had formed a previously undisclosed partnership with GlobalFoundries. Out of public view, the partnership had been able to build a first-of-its-kind manufacturing process for photonic quantum chips. This manufacturing process produces 300-millimeter wafers containing thousands of single photon sources, and a corresponding number of single photon detectors.

PsiQuantum chose to use photons to build its quantum computer for several reasons:

**Photons do not feel heat and most photonic components operate at room temperature.

**PsiQuantum’s superconducting quantum photon detectors require cooling, but operate at a temperature around 100 times hotter than superconducting qubits

**Photons aren’t affected by electromagnetic interference

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## Quantum technology reaches unprecedented control over captured light

A major obstacle towards the realization of a practically useful quantum computer is that the quantum systems used to encode the information are prone to noise and interference, which causes errors. Correcting these errors is a key challenge in the development of quantum computers. A promising approach is to replace qubits with resonators.

However, controlling the states of a resonator is a challenge with which quantum researchers all over the world are grappling. And the results from Chalmers provide a way of doing so. The technique developed at Chalmers allows researchers to generate virtually all previously demonstrated quantum states of light, such as for example Schrödinger’s cat or Gottesman-Kitaev-Preskill (GKP)states, and the cubic phase state, a state previously described only in theory.

“The cubic phase state is something that many quantum researchers have been trying to create in practice for twenty years. The fact that we have now managed to do this for the first time is a demonstration of how well our technique works, but the most important advance is that there are so many states of varying complexity and we have found a technique that can create any of them,” says Marina Kudra, a doctoral student at the Department of Microtechnology and Nanoscience and the study’s lead author.

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## DOE Grants $400,000 to Stony Brook University professor’s quantum computing research

The two-year DOE grant of $400,000 was awarded to the school’s computer science assistant professor Supartha Podder effective September 1. Podder’s research will specifically focus on quantum witnesses, or pieces of data that work to provide help and certify an answer to a given computation.

“My work looks to see if quantum computing is better than traditional computing types,” Podder explained in a press release. “We will do this by not only comparing quantum with classical in terms of standard resources such as time and space needed for computation but also in terms of broader and more abstract resources such as computational advice and witness.”

In order to better observe and understand quantum witnesses, Podder will work on designing new quantum algorithms and continue to investigate witnesses’ mechanical properties.

This grant supports the Biden administration’s larger plan to advance quantum computing research in the U.S. And because other countries have also invested in quantum research, federal agencies have recently focused on developing strong post-quantum cryptography and related standards for public and private networks to protect sensitive data from quantum computers’ potential encryption-cracking power

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Sandra K. Helsel, Ph.D. has been researching and reporting on frontier technologies since 1990. She has her Ph.D. from the University of Arizona.