#quantumprocesses

This science article describes a quantum optics breakthrough that distinguishes source radiation from vacuum fluctuations. Due to their unique causes, the researchers employed ultrafast laser pulses and nonlinear crystals to isolate these two phenomena, which were previously thought to be difficult to isolate in a lab. The scientists used phase-sensitive detection to show that certain radiation types correlate to certain light pulse quadratures, proving the fluctuation-dissipation theorem. These findings enable experiments on curved-space analogues, complex quantum processes, and entanglement harvesting. By making a long-standing thought experiment quantitative, we learn more about electromagnetic field-matter interactions.

Scientists Separate Quantum Coin Sides

Scientists at ETH Zürich have successfully detected and separated source radiation and vacuum fluctuations, a groundbreaking experiment in physics. In Nature Communications, the time-domain fluctuation-dissipation theorem is empirically proved at the quantum level for the first time, solving a century-old theoretical problem. A new doorway into sub-microscopic quantum electrodynamics was opened by the group using nonlinear crystals and ultrafast optics. This affects our understanding of black holes, the early cosmos, and quantum information.

The Empty Vacuum Mystery

To grasp this discovery's significance, define “empty” space. A vacuum is nothing in classical physics. Even at absolute zero, electromagnetic fields vary, and the vacuum is a sea of activity, according to quantum theory. Casimir effect, an attractive attraction between two uncharged metal surfaces, and Lamb shift, a minute energy change in an atom, are two well-known vacuum fluctuations-induced scientific phenomena.

Source radiation, or radiation response, happens with these changes. When an atom interacts with its radiative field, it "feels" its presence in the quantum field. Physicists have struggled to distinguish these effects for decades. The "two sides of the same quantum mechanical coin" were scientifically independent but empirically intertwined since they generally occur simultaneously and produce similar outcomes.

Relaunching Fermi's Thought Experiment

Fermi's 1932 Gedankenexperiment (thinking experiment) on the two-atom problem laid the groundwork for this finding. Fermi spotted two atoms in a vacuum—what if one “switched on” at any time?

Quantum theory describes two atom correlations. Initially, they may instantly interact with the surrounding field's vacuum oscillations over space. Second, a photon from one atom can reach the other at light speed. Despite its substantial discoveries, this thought experiment was impossible with actual atoms because to the difficulty of turning atomic interactions on and off quickly enough to see the time difference.

All-Optical Solution

Jérôme Faist and Alexa Herter led the ETH Zürich team in creating an all-optical duplicate of Fermi's setup to overcome these challenges. Instead of atoms, they used a zinc-telluride (ZnTe) nonlinear crystal and two ultra-short laser pulses.

The experiment was done in a cryostat frozen to 4 Kelvin to reduce thermal noise and ensure that only quantum signals were detected. Researchers were able to precisely “switch” the interaction on and off with pulses of 110 fs (quadrillionths of a second) and see causal effects.

The experiment was excellent because of phase-sensitive detection. Different laser pulse "quadratures" matched source radiation and vacuum fluctuations. They could switch between quarter-wave and half-wave plates in their detecting system to alter sensors to listen to source radiation or vacuum fluctuations separately.

Checking Fundamental Laws

Results stunningly confirmed quantum theory. When sensors were designed to detect vacuum fluctuations, correlations showed up symmetrically around zero-time delay to indicate their non-local, instantaneous nature. When set to source radiation, this radiation must follow causality rules and spread at a specific rate because the signal became asymmetric and only appeared at a certain time.

The results showed that the fluctuation-dissipation theorem may be experimentally validated. This fundamental law of physics states that a system's fluctuations (the vacuum's “noise”) are directly connected with their source radiation-induced dissipation (the “drag”). Source radiation signal was a Hilbert transform, or perfect mathematical reflection, of vacuum fluctuation signal, researchers found.

Black Holes to Quantum Computers: Why It Matters Distinguishing these two forces improves theoretical clarity and opens up new research avenues:

Scientists plan to “mine” the vacuum for quantum entanglement, needed for ultra-secure communication and quantum computers. This experiment shows that we can distinguish “harvested” entanglement from radiation exchange entanglement.

Curved Spacetime Analogies: The experimental setup can replicate an expanding cosmos or black hole event horizon conditions. Researchers could study Hawking radiation in a lab.

Quantum Information: Understanding the sub-picosecond periods during which information travels through the quantum vacuum will help scientists build noise-resistant quantum systems.

Vacuum fluctuations

In empty space, quantum physics causes vacuum fluctuations, tiny, unpredictable energy changes.

A plain explanation

A vacuum is a true empty space in classical physics.

Bard physicist received $500,000 to stabilize unstable quantum computers in the Hudson Valley.

Abhinav Prem, a Bard College physics assistant professor, received a prestigious two-year, $500,000 DOE research award, boosting the Hudson Valley's burgeoning “quantum footprint.” The award aims to solve quantum computers' inherent instability, one of science's biggest concerns. The project's main institution, Bard College, will receive $300,006, confirming its standing as a leading theoretical physics center.

Challenge of Quantum Fragility Scientific and engineering problems include creating devices that can maintain these sensitive states long enough to perform complex calculations. This is a difficult sector where “bold promises coexist with healthy skepticism,” as the goal of constructing a truly fault-tolerant system that regularly gives a real-world advantage has not yet been attained.

A Novel Approach: The “Runaway Train” Comparison Professor Abhinav Prem addresses stability difficulties with an innovative theoretical strategy. His work forces errors into predictable “paths,” rather than trying to block out all outside noise, which is physically demanding. Abhinav Prem uses mathematical symmetries and odd phases of matter to find and rectify errors before they threaten the system.

Abhinav Prem compares his technique to “building tracks for a runaway train” to illustrate this tough concept. The tracks constrain the "train" (the error) to a specific course so it cannot spread uncontrollably or harmfully. Predictable fault paths help build more resilient quantum structures.

Hudson River “Quantum Corridor” strengthening This research affects beyond Bard College laboratory. The research combines theoretical investigations with practical techniques for “near-term” devices. The research is supposed to have real ramifications for contemporary quantum technologies, not just theoretical.

The prize will also support future scientists by paying one Bard and one USC postdoctoral researcher. Our work supports the Hudson River's growing quantum knowledge. Sources say Abhinav Prem's work enhances the region's quantum footprint, which includes:

IBM Poughkeepsie quantum processes. The IBM Thomas J. Watson Research Center in Yorktown Heights conducts research.

Future Path Quantum computing is essential to the nation's scientific goals, as shown by the Department of Energy's sponsorship. There are still several barriers to building a reliable quantum computer. Building fault-tolerant computers with a “consistent real-world advantage” remains the community's top issue.

To make quantum computers a mainstay of modern business, Professor Abhinav Prem's work at Bard College must bridge advanced theoretical physics and practical engineering. The research focuses on machine stability and dependability to transition quantum computing from a fragile experimental field into a global innovation tool.

The Annandale-on-Hudson neighborhood celebrates, but the scientific community will wait to see if Abhinav Prem's “tracks” can stop quantum errors. The DOE's investment supports Hudson Valley theoretical frameworks for now.

Massive Colloidal Quantum Dots

Best Weak Coherent State Systems Lose to Imperfect Photon Sources in Quantum Key Distribution

Two new methods enable easily accessible, imperfect SPS to outperform weak coherent state (WCS) systems in quantum key distribution (QKD). This discovery potentially revolutionise QKD without flawless single-photon emitters by tackling a long-standing secure quantum communication problem.

QKD is crucial for safe optical communication in the quantum computing era. It uses quantum physics to create cryptographic keys between parties. Information should be encoded onto pure single-photon states for optimal security.

However, the lack of perfect SPS, which are challenging to create and maintain, has historically impeded the practical implementation of Quantum Key Distribution QKD. Perfect sources prevent photon number splitting (PNS) assaults and other advanced eavesdropping methods. Since multi-photon emissions reduce the efficacy of simple QKD approaches, realistic SPS purity and emission rate must meet tight criteria.

QKD systems often use attenuated lasers creating weak coherent state (WCS) due to the difficulty of developing stable, optimum SPS systems for practical application. WCS is more accessible yet has limitations. A pulse's possibility of emitting multiple photons is never zero due to its Poissonian photon distribution.

This renders them vulnerable to PNS attacks since eavesdroppers can collect multi-photon pulses and extract data unnoticed. WCS's secure key rate (SKR) is also limited by a high vacuum state probability and photon number emission probability dependence.

WCS systems have advanced decoy-state procedures to address these issues. These methods improve PNS attack detection and communication channel characterisation by changing photon distributions. Despite enhanced decoy-state techniques, WCS effectiveness is limited by Poissonian statistics and the fundamental relationship between photon number probabilities. It established the transmission distance "frontier" and secure key rates.

Yuval Bloom, Yoad Ordan, Tamar Levin, Kfir Sulimany, Eric G. Bowes, Jennifer A. Hollingsworth, and Ronen Rapaport define the new research as “radically different, more realistic approach” in PRX Quantum. Instead of perfect SPS, the team uses defective sources' regulated, sub-Poissonian photon statistics. They source single photons at ambient temperature using nanoantennas and gigantic colloidal quantum dots (gCQDs).

Due to their shortened photon-number Fock space, which can only include zero, one, or two photons (N=0, 1, or 2) and has a negligible probability of more than two photons, these gCQDs emit a biexciton-exciton (BX-X) cascade The optical excitation power may be simply modified to control the odds of obtaining these Fock states.

Two new QKD techniques have been put out and shown to work experimentally:

Decoy State on Truncated Fock Basis (DTB): Alice, the sender, smoothly controls SPS excitation level, alternating intensities for diverse photon statistics. Instead than being used for the secure key itself, these “decoy states” are employed to describe the channel and identify eavesdropping. Due to the reduced photon-number basis of the giant colloidal quantum dot gCQD, a precise analysis of the channel characteristics may be performed using only two decoy states, which is a major benefit over WCS techniques. WCS protocols, on the other hand, are either limited to two decoy states or require an infinite number for an exact answer. The maximal channel loss (MCL) was clearly improved by about 2 dB over WCS with unlimited decoy states when BB84 QKD was experimentally simulated with a basic gCQD employing DTB. With optimized gCQD devices (SPS1), theoretical studies indicate an even higher MCL increase of over 3 dB. Because of this, the DTB protocol is on par with or better than optimum WCS protocols and even cutting-edge cryogenic SPS. The method outperforms WCS even when using SPS with single photon purities as low as ~65% and g(2)(0) values as high as ~0.6. Heralded Purification (HP): In order to maximize the likelihood of two-photon emission (P2), Alice runs the SPS in the saturation regime at a single, high excitation power. A beam-splitter (BS) and a single photon detector (SPD) are employed as a purification step before to the BB84 encoding unit. A detection event at Alice’s detector essentially removes multi-photon events since emissions with N>2 photons are minimal. This results in an effectively pure single-photon source (where the effective two-photon probability P̃2 is close to zero) for that particular pulse. A lower signal rate is the price paid for this. Because of the extremely low effective two-photon probability (P̃2), realistic calculations utilizing an SPS2 device (gCQD on a hybrid nanocone-antenna) showed that BB84+HP allows for a greater MCL (~1 dB) compared to WCS with unlimited decoy states. Although the low P2 of the bare giant colloidal quantum dot gCQD prevented testing results with a bare gCQD from outperforming WCS with decoy, the potential for optimized devices (SPS2) is substantial.

Third-order correlation measurements demonstrated that three-photon emission probabilities are extremely small supporting the truncated Fock basis assumption. Experimental validation using a bare giant colloidal quantum dot gCQD verified the viability of controlling photon emission by varying laser intensity.

By avoiding the strict single-photon purity criteria that have long prevented the broad deployment of SPS, these protocols offer a realistic and feasible solution to create innovative photon sources with higher QKD performance. Their utility is further increased by the use of small, room-temperature, and readily integrated SPS devices, such as giant colloidal quantum dots gCQDs.

UChicago receives $21 million for a quantum engineering and health facility.

The Berggren Centre

The University of Chicago Berggren Centre for Quantum Biology and Medicine will launch a major research endeavour. On June 5, 2025, philanthropist Thea Berggren contributed £16.7 million ($21 million) to this historic project. In order to change the future of medicine, the centre is well-positioned to create a new discipline that blends biological research with quantum technology.

The Berggren Centre uses quantum engineering to peek into the human body in unprecedented ways. Our goal is to unlock previously unattainable insights into biology and illness to develop groundbreaking new medicines and diagnostics.

“The founding of the Berggren Centre is a testament to a strong belief: that the most profound scientific discoveries often arise when we combine disparate fields in daring new ways,” said University of Chicago president Paul Alivisatos. He added that the center's work could change how we view health and illness by combining medicine and quantum engineering.

The centre will benefit from the University's strengths in clinical care, biomedical research, and quantum science due to its position at the prestigious UChicago Pritzker School of Molecular Engineering (UChicago PME). UChicago PME dean Nadya Mason stressed the center's role in bringing together academics from different departments to set a new standard for patient care. For her creative approach to human health, she thanked Thea Berggren.

The Berggren Centre was founded to promote a new generation of “bilingual scholars” skilled in quantum physics and medicinal research:

Develop innovative quantum instruments for biomedical applications.

Scientists and engineers, these experts can practically apply quantum advances. The generous grant will fund workshops, fellowships, and conferences for multidisciplinary researchers to build an international quantum biology and medicine community. This pledge includes continuous help and endowment monies for sustainability.

This creative endeavour is already being led by UChicago scholars. Professor Alexander T. Pearson, Assistant Professor Peter Maurer, and Professor Aaron Esser-Kahn of Immunoengineering, for instance, are working together to develop quantum-enabled IDs that can track individual immune cells in real time. Thousands of cells could be monitored at once by this technique, providing fresh perspectives on cancer and inflammation and facilitating more individualised, targeted therapy.

The center’s goal is to make sure that quantum innovations are successfully transferred from the lab bench to the patient’s bedside. Using UChicago Medicine’s capabilities in clinical care and biomedical research, this will be accomplished. To create a workforce that can diagnose and treat diseases in new ways, Executive Vice President for Medical Affairs Mark Anderson says the centre will support cutting-edge educational initiatives, including a quantum pathway for aspiring and practicing physician-scientists.

The Berggren Centre will be co-directed by Julian Solway, a professor of medicine and the founding head of the Institute for Translational Medicine, and Greg Engel, a professor in the Department of Chemistry and at UChicago PME. Engel and Solway have previously worked together through the NSF Quantum Leap Challenge Institute for Quantum Sensing for Biophysics and Bioengineering (QuBBE), which seeks to create quantum imaging instruments that go beyond the bounds of classical approaches. With a particular emphasis on increasing clinical effect, the new centre will expand on this basis.

“It’s no easy task to integrate quantum physics and medicine, but it leads to tools and discoveries we never imagined possible,” Engel, whose work focusses on novel approaches to monitor, quantify, and manipulate quantum dynamics, said. In order to better human health, he thinks this gift will help bring together two very different scientific cultures. According to Solway, who has devoted his professional life to creating cooperative structures that would speed up medical research, the Berggren Centre is the next step forward in translational science. Quantum physicists, engineers, and physicians are collaborating to develop a new scientific language that could revolutionise our understanding and management of illness.

When Berggren visited the Atacama Desert, the idea for his present came to him. As she talked to astronomers who were motivated by the idea that quantum mechanics might help shape our future knowledge of the universe, she wondered about another possibility: What if the same quantum concepts were used to explain cellular physiology and disease? Berggren identified the University of Chicago as the perfect location to realise this ambition, calling the potential to revolutionise medicine “extraordinary.”

Although biological systems have historically been believed to disturb delicate quantum states in warm, loud settings, new research indicates that biological entities may potentially take advantage of quantum processes. The center’s research will investigate these possibilities in an effort to find new quantum-biological mechanisms that may be altered to provide therapeutic effects.

A worldwide understanding that the intersection of quantum science and health is a crucial area for 21st-century research is in line with the lofty objectives of the Berggren Centre. By fusing basic biological enquiries with quantum-enabled technology, UChicago hopes to empower researchers and clinicians, resulting in more accurate medicines, earlier disease detection, and ultimately, revolutionary patient care.

The Berggren Center’s founding represents a turning point in the fusion of medicine and physics. The centre will host quantum-enabled therapeutic discoveries thanks to inventive philanthropy, cutting-edge expertise, and strong institutional backing. By emphasising multidisciplinary interaction, training, and clinical translation, it establishes a new framework for bringing together scientific fields to address health challenges and ushers in quantum mechanical precision medicine.