# Category Archives: Quantum Physics

## When quantum physicists met Freud and Jung – IAI

Quantum mechanics and psychoanalysis entered the intellectual scene at roughly the same time. Several quantum physicists, shocked by the apparent consequences of their work and the strange irrationality at the heart of reality, sought the aid of psychoanalysts such as Freud and Jung to help them cope with their disturbing insights. The connection between quantum mechanics and psychoanalysis may not end there. There may be a deep link between the human mind, the unconscious and quantum reality we perceive. Writes Max Rogers, Jim Baggott and the late John Heilborn.

Historian and philosopher of science John Heilbron has died aged 89 in November 2023. An author of over 20 books, ranging from geometry electromagnetism to Galileo and quantum physics, was a renowned expert in the history of science. In the 1960s, he became the first graduate student of the philosopher Thomas Kuhn. As his student, John helped Kuhn prepare his seminal work

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## Quantum Magic: How Super Photons Are Shaping the Future of Physics – SciTechDaily

Artists view of a photonic Bose-Einstein condensate (yellow) in a bath of dye molecules (red) that has been perturbated by an external light source (white flash). Credit: A. Erglis/Albert-Ludwigs University of Freiburg

Researchers at the University of Bonn have demonstrated that super photons, or photon Bose-Einstein condensates, conform to fundamental physics theorems, enabling insights into properties that are often difficult to observe.

Under suitable conditions, thousands of particles of light can merge into a type of super photon. Physicists call such a state a photon Bose-Einstein condensate. Researchers at the University of Bonn have now shown that this exotic quantum state obeys a fundamental theorem of physics. This finding now allows one to measure properties of photon Bose-Einstein condensates which are usually difficult to access. The study was published on June 3 in the journal Nature Communications.

If many atoms are cooled to a very low temperature confined in a small volume, they can become indistinguishable and behave like a single super particle. Physicists also call this a Bose-Einstein condensate or quantum gas. Photons condense based on a similar principle and can be cooled using dye molecules. These molecules act like small refrigerators and swallow the hot light particles before spitting them out again at the right temperature.

In our experiments we filled a tiny container with a dye solution, explains Dr. Julian Schmitt from the Institute of Applied Physics at the University of Bonn. The walls of the container were highly reflective. The researchers then excited the dye molecules with a laser. This produced photons that bounced back and forth between the reflective surfaces. As the particles of light repeatedly collided with dye molecules, they cooled down and finally condensed into a quantum gas.

This process still continues afterward, however, and the particles of the super photon repeatedly collide with the dye molecules, being swallowed up before being spat out again. Therefore, the quantum gas sometimes contains more and sometimes less photons, making it flicker like a candle. We used this flickering to investigate whether an important theorem of physics is valid in a quantum gas system, says Schmitt.

This so-called regression theorem can be illustrated by a simple analogy: Let us assume that the super photon is a campfire that sometimes randomly flares up very strongly. After the fire blazes particularly brightly, the flames slowly die down and the fire returns to its original state. Interestingly, one can also cause the fire to flare up intentionally by blowing air into the embers. In simple terms, the regression theorem predicts that the fire will then continue to burn down in the same way as if the flare up had occurred at random. This means that it responds to the perturbation in exactly the same way as it fluctuates on its own without any perturbation.

Blowing Air Into a Photon Fire

We wanted to find out whether this behavior also applies to quantum gases, explains Schmitt, who is also a member of the transdisciplinary research area (TRA) Building Blocks of Matter and the Matter and Light for Quantum Computing Cluster of Excellence at the University of Bonn. For this purpose, the researchers first measured the flickering of the super photons to quantify the statistical fluctuations. They then figuratively speaking blew air into the fire by briefly firing another laser at the super photon. This perturbation caused it to briefly flare up before it slowly returned to its initial state.

We were able to observe that the response to this gentle perturbation follows precisely the same dynamics as the random fluctuations without a perturbation, says the physicist. In this way we were able to demonstrate for the first time that this theorem also applies to exotic forms of matter as quantum gases. Interestingly, this is also the case for strong perturbations. Systems usually respond differently to stronger perturbations than they do to weaker ones an extreme example is a layer of ice that will suddenly break when the load placed on it becomes too heavy. This is called nonlinear behavior, says Schmitt. However, the theorem remains valid in these cases, as we have now been able to demonstrate together with our colleagues from the University of Antwerp.

The findings are of huge relevance for fundamental research with photonic quantum gases because one often does not know precisely how they will flicker in their brightness. It is much easier to determine how the super photon responds to a controlled perturbation. This allows us to learn about unknown properties under very controlled conditions, explains Schmitt. It will enable us, for example, to find out how novel photonic materials consisting of many super photons behave at their core.

Reference: Observation of nonlinear response and Onsager regression in a photon Bose-Einstein condensate by Alexander Sazhin, Vladimir N. Gladilin, Andris Erglis, Gran Hellmann, Frank Vewinger, Martin Weitz, Michiel Wouters and Julian Schmitt, 3 June 2024, Nature Communications. DOI: 10.1038/s41467-024-49064-9

The Institute of Applied Physics at the University of Bonn, the University of Antwerp (Belgium) and the University of Freiburg participated in the study. The project was supported by the German Research Foundation (DFG), the European Union (ERC Starting Grant), the German Aerospace Centre (DLR) and the Belgium funding agency FWO Flanders.

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Quantum Magic: How Super Photons Are Shaping the Future of Physics - SciTechDaily

## What "naked" singularities are revealing about quantum space-time – New Scientist

Adobe Stock/Erika Eros/Alamy/Collage: Ryan Wills

Deep inside a black hole, the cosmos gets twisted beyond comprehension. Here, at some infinitesimal point of infinite density, the fabric of the universe gets so ludicrously warped that Albert Einsteins general theory of relativity, which describes how mass bends space-time, ceases to make sense. At the singularity, our understanding falls apart.

As daunting as singularities are, each one is at least safely tucked away inside the event horizon of a black hole, the boundary beyond which we cant see. This not only cloaks them from view, but also stops unknown effects they herald, namely the horrors of unpredictability, from leaching out into the wider universe. But what if singularities could exist outside black holes after all?

That question, given fresh impetus in recent years by demonstrations that general relativity allows for this, has spurred theorists to probe singularities from a deeper perspective, folding in insights from the latest forays into the possible quantum foundations of gravity. Already, they are realising that this new approach flips the script on how we think about singularities, says Netta Engelhardt at the Massachusetts Institute of Technology.

Fair warning: the work takes us into some labyrinthine physics. But by grappling with singularities in this way, Engelhardt and her colleagues are deciphering the enigmatic connections between the quantum realm and classical gravity and reinforcing the revolutionary idea that

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What "naked" singularities are revealing about quantum space-time - New Scientist

## New Method Enhances the Accuracy of Quantum Calculations – AZoQuantum

In an article recently published in the journal Communications Physics, researchers investigated the feasibility of calculating high-accuracy, finite-size effect-free hyperfine tensors using an improved integration method for the case of the nitrogen-vacancy (NV) center in diamond.

Point defects are widely utilized to manipulate the electronic and optical characteristics of semiconductors. Recently, the introduction of paramagnetic defects has begun to alter the magnetic properties of these materials, revealing a range of mesoscopic and microscopic magnetic phenomena.

By reducing the concentration of defects, controllable few-spin systems can be established, facilitating the creation of quantum nodes and qubits based on point defects. In wide-bandgap semiconductors, these point defect qubits exhibit robustness and high coherence, even at elevated temperatures.

The optically addressable spin qubits, exemplified by the silicon vacancy in silicon carbide and the NV center in diamond, maintain prolonged coherence times at room temperature. Consequently, point defect quantum devices are increasingly prominent in various quantum technology applications, including quantum internet and quantum sensin.

In light element semiconductors, the coherence of spin qubits is compromised by interactions with nuclear spins and paramagnetic defects. In high-purity samples, the magnetic environment of a spin qubit is predominantly influenced by the surrounding nuclear spin bath.

The interaction between point defect spins and nuclear spins is mediated through hyperfine coupling, which is determined by the positions of the nuclear spins and the spatial distribution of the defect's spin density. The hyperfine tensor, which parameterizes the hyperfine term in the spin Hamiltonian, is crucial in this interaction. The elements of the hyperfine tensor can be both calculated using first-principles electronic structure methods and measured via various magnetic resonance techniques.

While the accuracy of the calculated hyperfine tensors or parameters is impressive for nuclear spins close to the defectwithin 1-5 the precision diminishes significantly for nuclear spins positioned at greater distances. This decrease in accuracy is largely due to periodic boundary conditions and the limitations of finite-size effects.

In this study, researchers employed a first-principles code, widely recognized in the industry, to demonstrate that the computed hyperfine parameters' absolute relative error can surpass 100% for the NV center in diamond. They initially showcased the numerical inaccuracies in the hyperfine parameters using the industry-standard VASP code.

To address the methodological shortcomings, the team introduced a real-space integration method and employed a substantially large support lattice that accounted for nuclear spins beyond the supercell boundaries. They conducted extensive calculations for the NV center in diamond using different exchange-correlation functionals and benchmarked their results against existing experimental hyperfine datasets.

For these calculations, diamond supercells containing 1728 and 512 atoms with a central NV center were used. The researchers utilized the Heyd-Scuseria-Ernzerhof (HSE06) and Perdew-Burke-Ernzerhof (PBE) exchange-correlation functionals, applied stringent convergence criteria, and performed -point sampling of the Brillouin zone with a 500 eV cutoff energy for the plane-wave basis set.

The energy threshold for the self-consistent field calculations was set at 10-6 eV for the self-consistent field calculations, and the defect structure was optimized until the most significant force fell below 10-3 eV/. For the hyperfine tensor calculations in real space, the convergent spin density from the 1728-atom supercell model was utilized. This model was defined on a finely spaced real-space grid of 0.036 , processed through VASP.

By implementing the proposed method, researchers achieved a significant enhancement in hyperfine values, achieving a nearly 100-fold reduction in the mean absolute relative error (MARE) compared to the industry-standard VASP code. This substantial improvement was characterized by markedly lower relative mean errors across all measured distances.

In particular, the application of the Heyd-Scuseria-Ernzerhof (HSE06) functional with a 0.2 mixing parameter demonstrated optimal performance for the NV center in diamond, yielding a mean absolute percentage error of just 1.7 % for nuclear spins located 6-30 from the NV center. This performance markedly surpassed previous theoretical predictions using VASP, indicating a significant advancement in the accuracy of hyperfine calculations.

The study further highlighted that the remaining discrepancies in the results could likely be attributed to inaccuracies in calculating the Fermi contact term. Moreover, researchers provided highly accurate hyperfine tensors for 104 lattice sites and volumetric hyperfine data with a spatial resolution finer than 0.1 . This level of precision is critical for the high-accuracy simulation of NV center quantum nodes, which are pivotal in quantum information processing and for accurately positioning nuclear spins through the comparison of experimental and theoretical hyperfine data.

In summary, this study confirmed that high-accuracy, finite-size effect-free hyperfine tensors can be computed effectively using the proposed integration method. These findings suggest that even more precise theoretical hyperfine data could be obtained by further enhancing numerical accuracy in larger supercells and incorporating more precise experimental data.

Takcs, I., Ivdy, V. (2024). Accurate hyperfine tensors for solid state quantum applications: Case of the NV center in diamond. Communications Physics, 7(1), 1-6. https://doi.org/10.1038/s42005-024-01668-9, https://www.nature.com/articles/s42005-024-01668-9

Disclaimer: The views expressed here are those of the author expressed in their private capacity and do not necessarily represent the views of AZoM.com Limited T/A AZoNetwork the owner and operator of this website. This disclaimer forms part of the Terms and conditions of use of this website.

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New Method Enhances the Accuracy of Quantum Calculations - AZoQuantum

## CERN welcomes International Year of Quantum Science and Technology – CERN

On the centenary of quantum mechanics -- the bedrock of particle physics and enabler of numerous technologies CERN is contributing to the development of a new generation of quantum technologies for fundamental research and beyond.

100 years ago, a handful of visionary physicists upturned notions about nature that had guided scientists for centuries. Particles can be point- or wave-like, depending on how you look at them. Their behaviour is probabilistic and can momentarily appear to violate cherished laws such as the conservation of energy. Particles can be entangled such that one feels the change of state of the other instantaneously no matter the distance between them, and, as befalls Schrdinger's famous cat, they can be in opposite states at the same time.

Today, thanks to pioneering theoretical and experimental efforts to understand this complex realm, physicists can confidently navigate through such apparently irrational concepts. Quantum theory has not only become foundational to physics, chemistry, engineering and biology, but underpins the transistors, lasers and LEDs that drive modern electronics and telecommunications -- not to mention solar cells, medical scanners and global positioning systems. But this is only the beginning.

On 7 June the United Nations declared 2025 the International Year of Quantum Science and Technology to celebrate the contributions of quantum science to technological progress, raise awareness of its importance to sustainable development, and ensure that all nations have access to quantum education and opportunities. As the worlds largest particle physics lab, CERN has been interrogating the quantum theories that govern the microscopic world for the past 70 years. Most recently, it has entered the rapidly growing domain of quantum technologies, which aims to harness the strangest aspects of quantum mechanics to build a new generation of quantum devices for fundamental research and beyond.

In recent years, we have learned not just to use the properties of the quantum world but, also, to control them, explains Sofia Vallecorsa, coordinator of the CERN Quantum Technology Initiative (QTI). Today, the revolution is all about controlling individual quantum systems, such as single atoms or ions, enabling even more powerful applications.

At CERN, quantum technologies are studied and developed through two initiatives: the QTI, whose aim is to enable technologies such as quantum computing, quantum state sensors, time synchronisation protocols, and many more for high-energy physics activities; and the recently established Open Quantum Institute (OQI), whose aim is to identify, support and accelerate the development of future societal applications benefiting from quantum computing algorithms.

One of the most promising fields is quantum computing. Unlike conventional computers that use bits that can be in one of just two states, quantum computers using qubits which can exist in superpositions of states. This enables a vast number of computations to be processed simultaneously, offering important applications in fields such as cryptography, logistics and process optimisation, and drug discovery. Quantum communication, which exploits the principles of quantum mechanics to make it impossible to intercept information without detection, is another significant area of development. A third pillar of CERNs quantum-technologies programme is sensing to allow ultra-precise measurements of physical quantities, with potential applications in fields including medicine, navigation and climate science.

What started 100 years ago as a purely theoretical physics investigation is now beginning to unleash its full potential, says OQI coordinator Tim Smith of CERN. The International Year of Quantum Science and Technology will be a wonderful opportunity to celebrate the past, the present and the future of our understanding of the quantum world.

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CERN welcomes International Year of Quantum Science and Technology - CERN

## Clash Between General Relativity and Quantum Mechanics Could Be Resolved by New Mathematical Framework – The Debrief

One of the greatest challenges in modern physics involves reconciling apparent conflicts between general relativity and quantum mechanics, which are largely viewed as incompatible due to their differing concepts of space and time.

However, innovative new research is finally suggesting that a resolution to these longstanding differences could be on the horizon, with the introduction of a more advanced mathematical framework that may finally help unite these two fundamental theories.

In general relativity, Einstein envisioned a gently curved spacetime, where time is relative to the perspective of an observer in relation to time and space. By comparison, the realm of quantum mechanics presents a chaotic view of the universe on the microscopic scale, where time is essentially absolute and universal.

Because of these issues, Einstein had a somewhat turbulent relationship with the theory of quantum mechanics, which, ironically, resulted largely from work by Erwin Schrdinger that drew from Einsteins later studies of atoms, molecules, and light. The apparent random chaos inherent in quantum mechanics prompted one of Einsteins most famous axioms, where he expressed that God does not play dice with the universe, also insisting that perfect laws in the world of things existing as real objects seemingly in contrast to the chaotic and unpredictable nature of quantum physics.

However, new research is offering fresh insights into the long-held divide between these differing perspectives of our universe.

According to Einsteins theory, gravity is not a force but emerges due to the geometry of the four-dimensionalspacetime continuum, or spacetime for short, says researcher Sjors Heefer, whose recent Ph.D. research involved studies of gravity that have not only led to new possibilities in gravity wave research but also to a potential reconciliation between the quantum and relativistic worlds.

At the heart of Heefers research, which explores the role of gravity on a universal scale, is the relationship between matter and spacetime. An often relied-on summary of Einsteins general theory of relativity dictates that matter tells spacetime how to curve, and curved spacetime tells matter how to move. However, this well-defined way of explaining gravity in general relativity falls short when it comes to quantum mechanics.

Heefers focus on gravitational waves examines their implications in relativistic terms and quantum mechanics. Gravitational waves arise from the curvature in spacetime that Einstein envisioned and are essentially the ripples caused by massive objects or events like stellar collisions and black holes.

In quantum mechanics, particles differ significantly from the relativistic view in that they can exist simultaneously in multiple states until they collapse at random into a single state when under observation. This mysterious probabilistic nature is observed in all matter and forces in the universe, except for gravity, a fact that presents one of the most significant challenges for modern physicists.

One potential way of resolving the issue would involve an expansion of the current mathematical framework used to describe general relativity. Although traditionally physicists have relied on what is known as pseudo-Riemannian geometry for describing relativistic phenomena, recent research has increasingly pointed to a more advanced mathematical language known as Finsler geometry as being better equipped at expressing the profound oddity of our universe.

In physics, fields describe values at each point in space and time, whereas gravitational fields represent the curvature of spacetime. In his Ph.D. research, Heefer delved into the challenging work of attempting to solve field equations in Finsler gravity, specifically looking at the vacuum field equation of Christian Pfeifer and Mattias N. R. Wohlfarth, an equation that relates to governing the gravitational field in empty space. Specifically, the equation describes the potential shapes spacetime geometry may take when no matter is present.

To good approximation, this includes all interstellar space between stars and galaxies, as well as the empty space surrounding objects such as the sun and the Earth, Heefer said in a recent statement. By carefully analyzing the field equation, several new types of spacetime geometries have been identified.

According to Heefers research, observations of gravitational waves in recent years do appear to complement the hypothesis that spacetime works in accordance with Finsler gravity, presenting an expanded mathematical framework that could potentially also help to reconcile the seemingly disparate worlds of general relativity and quantum mechanics.

While Heefers findings are promising, they represent only the beginning of exploring Finsler gravitys implications, as well as efforts to resolve the relativistic and quantum worlds.

However, Heefer says he is optimistic that our results will prove instrumental in deepening our understanding of gravity, adding that he hopes that with time, they may even shine light on the reconciliation of gravity with quantum mechanics.

Heefers research is outlined in Finsler Geometry, Spacetime & Gravity, recently published by the Eindhoven University of Technology in the Netherlands.

Micah Hanks is the Editor-in-Chief and Co-Founder of The Debrief. He can be reached by email atmicah@thedebrief.org. Follow his work atmicahhanks.comand on X:@MicahHanks.

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## Quantum computer photons create a vortex when they collide – Earth.com

Scientists have stumbled upon a remarkable discovery that challenges our understanding of the quantum world. New research revealed the existence of a previously unknown type of vortex that emerges when photons, the elusive particles of light, engage in a mesmerizing dance of interaction.

The implications of this finding extend far beyond the realm of pure science, holding the potential to revolutionize the field of quantum computing.

The research team, led by a brilliant quartet of scientists Dr. Lee Drori, Dr. Bankim Chandra Das, Tomer Danino Zohar, and Dr. Gal Winer embarked on this journey of discovery in the hallowed halls of Prof. Ofer Firstenbergs laboratory at the Weizmann Institute of Sciences Physics of Complex Systems Department.

Their initial goal was to explore efficient ways of harnessing the power of photons for data processing in quantum computers.

Little did they know that their quest would lead them down an unexpected path, into a world where the rules of classical physics are bent and the secrets of the quantum realm are laid bare.

Photons, the fundamental particles of light, are known for their wave-like behavior. However, getting them to interact with each other is no easy feat. It requires the presence of matter that acts as an intermediary.

To create the perfect environment for photon interactions, the researchers designed a unique setup: a 10-centimeter glass cell containing a dense cloud of rubidium atoms, tightly packed in the center.

As photons passed through this cloud, the researchers closely examined their state to see if they had influenced one another.

When the photons pass through the dense gas cloud, they send a number of atoms into electronically excited states known as Rydberg states, Prof. Firstenberg explains.

He goes on to describe how, in these Rydberg states, a single electron within the atom begins to orbit at an astonishing distance, up to 1,000 times the diameter of an unexcited atom.

This electron, with its vastly expanded orbit, generates an electric field so powerful that it envelops and influences countless neighboring atoms, effectively transforming them into what Prof. Firstenberg poetically refers to as an imaginary glass ball.'

As the researchers delved deeper into the interactions between photons, they stumbled upon something extraordinary.

When two photons passed relatively close to each other, they moved at a different speed than they would have if each had been traveling alone. This change in speed altered the positions of the peaks and valleys of the waves they carried.

In the ideal scenario for quantum computing applications, the positions of the peaks and valleys would become completely inverted relative to one another, a phenomenon known as a 180-degree phase shift. However, what the researchers observed was even more fascinating.

When the gas cloud was at its densest and the photons were in close proximity, they exerted the highest level of mutual influence.

But as the photons moved away from each other or the atomic density around them decreased, the phase shift weakened and disappeared.

Instead of a gradual process, the researchers were surprised to find that a pair of vortices developed when two photons were a certain distance apart.

To visualize photon vortices, imagine dragging a vertically held plate through water. The rapid movement of the water pushed by the plate meets the slower movement around it, creating two vortices that appear to be moving together along the waters surface.

In reality, these vortices are part of a three-dimensional configuration called a vortex ring.

The researchers discovered that the two vortices observed when measuring two photons are part of a three-dimensional vortex ring generated by the mutual influence of three photons.

These findings showcase the striking similarities between the newly discovered vortices and those found in other environments, such as smoke rings.

While the discovery of photon vortices has taken center stage, the researchers remain dedicated to their original goal of advancing quantum data processing.

The next phase of their study will involve firing photons into each other and measuring the phase shift of each photon separately.

The strength of these phase shifts could determine the potential for photons to be used as qubits, the basic units of information in quantum computing.

Unlike regular computer memory units, which can only be 0 or 1, quantum bits have the ability to represent a range of values between 0 and 1 simultaneously.

The prevalent assumption was that this weakening would be a gradual process, but researchers were in for a surprise, Dr. Eilon Poem and Dr. Alexander Poddubny, key contributors to the study, reveal.

They go on to describe the astonishing discovery that when two photons reached a specific distance from each other, a pair of vortices spontaneously emerged.

These vortices, characterized by a complete 360-degree phase shift of the photons, featured a peculiar void at their center, eerily reminiscent of the dark, calm eye found at the heart of other well-known vortices in nature.

The journey that led to this discovery spanned eight years and saw two generations of doctoral students pass through Prof. Firstenbergs laboratory.

Over time, the Weizmann scientists successfully created a dense, ultracold gas cloud packed with atoms, enabling them to achieve the unprecedented: photons that underwent a phase shift of 180 degrees or more.

As the research team continues to unravel the mysteries of photon interactions and their potential applications in quantum computing, one thing is certain: their findings have opened up a new realm of possibilities in the world of physics and beyond.

The full study was published in the journal Science.

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Quantum computer photons create a vortex when they collide - Earth.com

## New technique could help build quantum computers of the future – EurekAlert

image:

Kaushalya Jhuria in the lab testing the electronics from the experimental setup used to make qubits in silicon.

Credit: Thor Swift/Berkeley Lab

Quantum computers have the potential to solve complex problems in human health, drug discovery, and artificial intelligence millions of times faster than some of the worlds fastest supercomputers. A network of quantum computers could advance these discoveries even faster. But before that can happen, the computer industry will need a reliable way to string together billions of qubits or quantum bits with atomic precision.

Connecting qubits, however, has been challenging for the research community. Some methods form qubits by placing an entire silicon wafer in a rapid annealing oven at very high temperatures. With these methods, qubits randomly form from defects (also known as color centers or quantum emitters) in silicons crystal lattice. And without knowing exactly where qubits are located in a material, a quantum computer of connected qubits will be difficult to realize.

But now, getting qubits to connect may soon be possible. A research team led by Lawrence Berkeley National Laboratory (Berkeley Lab) says that they are the first to use a femtosecond laser to create and annihilate qubits on demand, and with precision, by doping silicon with hydrogen.

The advance could enable quantum computers that use programmable optical qubits or spin-photon qubits to connect quantum nodes across a remote network. It could also advance a quantum internet that is not only more secure but could also transmit more data than current optical-fiber information technologies.

To make a scalable quantum architecture or network, we need qubits that can reliably form on-demand, at desired locations, so that we know where the qubit is located in a material. And that's why our approach is critical, said Kaushalya Jhuria, a postdoctoral scholar in Berkeley Labs Accelerator Technology & Applied Physics (ATAP) Division. She is the first author on a new study that describes the technique in the journal Nature Communications. Because once we know where a specific qubit is sitting, we can determine how to connect this qubit with other components in the system and make a quantum network.

This could carve out a potential new pathway for industry to overcome challenges in qubit fabrication and quality control, said principal investigator Thomas Schenkel, head of the Fusion Science & Ion Beam Technology Program in Berkeley Labs ATAP Division. His group will host the first cohort of students from the University of Hawaii in June as part of a DOE Fusion Energy Sciences-funded RENEW project on workforce development where students will be immersed in color center/qubit science and technology.

Forming qubits in silicon with programmable control

The new method uses a gas environment to form programmable defects called color centers in silicon. These color centers are candidates for special telecommunications qubits or spin photon qubits. The method also uses an ultrafast femtosecond laser to anneal silicon with pinpoint precision where those qubits should precisely form. A femtosecond laser delivers very short pulses of energy within a quadrillionth of a second to a focused target the size of a speck of dust.

Spin photon qubits emit photons that can carry information encoded in electron spin across long distances ideal properties to support a secure quantum network. Qubits are the smallest components of a quantum information system that encodes data in three different states: 1, 0, or a superposition that is everything between 1 and 0.

With help from Boubacar Kant, a faculty scientist in Berkeley Labs Materials Sciences Division and professor of electrical engineering and computer sciences (EECS) at UC Berkeley, the team used a near-infrared detector to characterize the resulting color centers by probing their optical (photoluminescence) signals.

What they uncovered surprised them: a quantum emitter called the Ci center. Owing to its simple structure, stability at room temperature, and promising spin properties, the Ci center is an interesting spin photon qubit candidate that emits photons in the telecom band. We knew from the literature that Ci can be formed in silicon, but we didnt expect to actually make this new spin photon qubit candidate with our approach, Jhuria said.

The researchers learned that processing silicon with a low femtosecond laser intensity in the presence of hydrogen helped to create the Ci color centers. Further experiments showed that increasing the laser intensity can increase the mobility of hydrogen, which passivates undesirable color centers without damaging the silicon lattice, Schenkel explained.

A theoretical analysis performed by Liang Tan, staff scientist in Berkeley Labs Molecular Foundry, shows that the brightness of the Ci color center is boosted by several orders of magnitude in the presence of hydrogen, confirming their observations from laboratory experiments.

The femtosecond laser pulses can kick out hydrogen atoms or bring them back, allowing the programmable formation of desired optical qubits in precise locations, Jhuria said.

The team plans to use the technique to integrate optical qubits in quantum devices such as reflective cavities and waveguides, and to discover new spin photon qubit candidates with properties optimized for selected applications.

Now that we can reliably make color centers, we want to get different qubits to talk to each other which is an embodiment of quantum entanglement and see which ones perform the best. This is just the beginning, said Jhuria.

The ability to form qubits at programmable locations in a material like silicon that is available at scale is an exciting step towards practical quantum networking and computing, said Cameron Geddes, Director of the ATAP Division.

Theoretical analysis for the study was performed at the Department of EnergysNational Energy Research Scientific Computing Center (NERSC) at Berkeley Lab with support from the NERSC QIS@Perlmutterprogram.

The Molecular Foundry and NERSC are DOE Office of Science user facilities at Berkeley Lab.

This work was supported by the DOE Office of Fusion Energy Sciences.

###

Lawrence Berkeley National Laboratory (Berkeley Lab) is committed to delivering solutions for humankind through research in clean energy, a healthy planet, and discovery science. Founded in 1931 on the belief that the biggest problems are best addressed by teams, Berkeley Lab and its scientists have been recognized with 16 Nobel Prizes. Researchers from around the world rely on the Labs world-class scientific facilities for their own pioneering research. Berkeley Lab is a multiprogram national laboratory managed by the University of California for the U.S. Department of Energys Office of Science.

DOEs Office of Science is the single largest supporter of basic research in the physical sciences in the United States, and is working to address some of the most pressing challenges of our time. For more information, please visitenergy.gov/science.

Nature Communications

Experimental study

Not applicable

Programmable quantum emitter formation in silicon

27-May-2024

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New technique could help build quantum computers of the future - EurekAlert

## Unifying Quantum Mechanics and Gravity – AZoQuantum

Jun 6 2024Reviewed by Lexie Corner

In a new study published in Advanced Photonics Nexus, an international team of researchers made significant strides in exploring the mysteries of quantum gravity. These findings shed new light on future research aimed at unifying quantum mechanics and general relativity.

This study will help solve one of contemporary physics most fundamental enigmas: reconciling Einsteins theory of gravity with principles of quantum mechanics.

For decades, scientists have been fascinated by the long-standing challenge of unifying these two pillars of physics. This has given rise to many theoretical frameworks, such as string theory and loop quantum gravity. However, without experimental evidence, these notions are theoretical.

How can the quantum nature of gravity be tested? Tangible methods to investigate the quantum behavior of the gravitational field have been developed in the last ten years (by Marletto and Vedral, and Bose et al.). These techniques were based on the idea of gravity-mediated entanglement.

The current study illustrates the concepts of gravity-mediated entanglement using light particles (i.e., photons). It utilizes state-of-the-art tools and techniques from quantum information theory and quantum optics.

The experiment uses photon interaction to simulate the influence of a gravitational field on quantum particles. Surprisingly, the photons' characteristics intertwine while never interacting, demonstrating nonlocality, a fundamental quantum phenomenon.

This entanglement mimics the expected behavior of gravity-induced entanglement and is mediated by another independent photonic feature, offering important new information on the quantum basis of gravity.

Most importantly, the study also tackles the difficulty of identifying the entanglement produced in these experiments. By addressing the limitations and noise sources inherent in such investigations, the researchers pave the way for clarifying concepts and tools for future studies targeted at directly witnessing gravity-mediated entanglement.

Gravity-mediated entanglement experiments can open a new chapter in the understanding of the fundamental properties of the universe.

The implications of this research are profound. It offers an experimental validation for the principles behind future quantum gravity experiments that will serve as litmus tests for competing theoretical frameworks.

Emanuele Polino, Study Author and Postdoctoral Scholar, Sapienza University

This remarkable finding represents a major step forward in understanding the secrets of quantum gravity, as physicists continue to push the frontiers of experimental and theoretical inquiry.

Polino, E., et al. (2024) Photonic implementation of quantum gravity simulator. Advanced Photonics Nexus. doi:10.1117/1.APN.3.3.036011

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## Simulating Quantum Circuits with Light-Induced Magnetism – AZoQuantum

Jun 12 2024Reviewed by Lexie Corner

Researchers from the Graz University of Technology have calculated how suitablemolecules can be excited by pulses of infrared light to generate magnetic fields. The research, published in the Journal of the American Chemical Society, will help in the construction of quantum computing circuits.

Molecules exposed to infrared radiation start to vibrate because of the energy source. This well-known phenomenon prompted Andreas Hauser of the Institute of Experimental Physics at Graz University of Technology (TU Graz) to investigate whether these oscillations could also be exploited to produce magnetic fields.

This is due to the positively charged nature of atomic nuclei and the creation of magnetic fields when charged particles move. Andreas Hauser and colleagues have now determined that, when infrared pulses operate on metal phthalocyanines, ring-shaped, planar dye molecules, these molecules generate minuscule magnetic fields in the nm range due to their high symmetry.

The calculations suggest that nuclear magnetic resonance spectroscopy could be used to determine the relatively low but highly accurately localized field strength.

The team used modern electron structure theory on supercomputers at the Vienna Scientific Cluster and TU Graz to calculate how phthalocyanine molecules behave when irradiated with circularly polarized infrared light.

They also drew on preliminary work from the early days of laser spectroscopy, some of which were decades old. The circularly polarized, or helically twisted, light waves excited two simultaneous molecular vibrations at right angles to one another.

As every rumba dancing couple knows, the right combination of forwards-backwards and left-right creates a small, closed loop. And this circular movement of each affected atomic nucleus actually creates a magnetic field, but only very locally, with dimensions in the range of a few nanometers.

Andreas Hauser, Institute of Experimental Physics, Graz University of Technology

According to Andreas Hauser, it is even possible to regulate the magnetic field's strength and direction by carefully adjusting the infrared light. As a result, the molecules would become high-precision optical switches that couldbe utilized to construct quantum computer circuits.

Andreas Hauser is working with colleagues at the TU Graz Institute of Solid-State Physics and a group at the University of Graz to demonstratethat controlled generation of molecule magnetic fields is possible.

For proof, but also for future applications, the phthalocyanine molecule needs to be placed on a surface. However, this changes the physical conditions, which in turn influences the light-induced excitation and the characteristics of the magnetic field, we therefore want to find a support material that has minimal impact on the desired mechanism.

Andreas Hauser, Institute of Experimental Physics, Graz University of Technology

Before testing the most promising versions in experiments, the physicist and his associates wish to compute the interactions between the deposited phthalocyanines, the support material, and the infrared light in a subsequent stage.

Wilhelmer, R., et al. (2024) Molecular Pseudorotation in Phthalocyanines as a Tool for Magnetic Field Control at the Nanoscale. Journal of the American Chemical Society. doi.org/10.1021/jacs.4c01915

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