How the 2012 APS March Meeting Redefined Reality
The Boston Convention Center buzzed with electric anticipation on February 27, 2012, as over 8,000 physicists converged for the American Physical Society's March Meeting. This annual pilgrimage—where condensed matter meets quantum mystery—became the staging ground for revelations that would reshape our understanding of the quantum world. Amidst sessions spanning graphene superconductivity to neutrino anomalies, a quiet revolution was unfolding: the race to prove quantum steering, a phenomenon Einstein dismissed as "spooky action at a distance." At the heart of this revolution stood an Australian team armed with superconducting sensors so precise, they would close one of quantum physics' most stubborn loopholes forever 1 .
Quantum steering occurs when one particle instantly influences another's state across vast distances—a phenomenon so counterintuitive that Schrödinger himself coined the term in 1935. Unlike classical physics, where objects possess definite properties, entangled particles exist in a shared probabilistic haze until measured. The 2012 APS meeting featured a dedicated Focus Session on Quantum Information for Quantum Foundations, exploring how information theory could finally tame these quantum paradoxes. Valerio Scarani's keynote on "Information Causality" set the stage: quantum correlations obey strict constraints that prevent faster-than-light communication, yet permit astonishing connections between particles 6 .
For decades, skeptics exploited a critical weakness in entanglement experiments: detection inefficiency. Traditional photon detectors missed 70-80% of particles, allowing skeptics to argue that observed correlations arose only from selective data filtering. Closing this loophole required detecting >50% of entangled pairs without post-selection—a feat deemed nearly impossible with 2012 technology. As Session X30 on "Foundational Experiments" convened, Marcelo de Almeida's team prepared to unveil their solution: superconducting transition edge sensors (TES) capable of catching 62% of photons—a quantum efficiency leap comparable to upgrading from dial-up to fiber optics .
The University of Queensland-NIST collaboration executed their experiment with surgical precision:
A laser fired at a nonlinear crystal, creating pairs of infrared photons (1,550 nm) linked in polarization—a process called spontaneous parametric down-conversion.
One photon ("Alice") went to a trusted detector under team control; the other ("Bob") traveled to an "untrusted" system mimicking a potentially dishonest device.
Superconducting niobium films chilled to 0.1°C above absolute zero detected photon-induced temperature spikes. Unlike conventional detectors, TES devices recorded photons without "click blindness" gaps.
Alice performed 320 polarization measurements, demanding Bob report matching results. Under classical physics, Bob could fake entanglement; under quantum rules, his responses would be constrained by nonlocal links.
| Detector Type | Efficiency | Dark Count Rate | Loophole Vulnerability |
|---|---|---|---|
| Traditional Avalanche Photodiode | ~30% | 100s/sec | High (post-selection required) |
| Superconducting Nanowire | ~40% | <10/sec | Moderate |
| Transition Edge Sensor (TES) | 62% | ~0.1/sec | None (loophole closed) |
The data table below reveals the statistical knockout punch delivered to quantum doubters:
| Measurement Basis | Classical Bound | Observed Value | Deviation (σ) |
|---|---|---|---|
| Rectilinear (0° vs 90°) | ≤1 | 1.308 ± 0.006 | 51.3σ |
| Diagonal (45° vs 135°) | ≤1 | 1.291 ± 0.006 | 48.5σ |
| Circular (L vs R) | ≤1 | 1.275 ± 0.007 | 39.3σ |
By violating the steering inequality by 48 standard deviations across all bases—far exceeding the 5σ threshold for discovery—the team confirmed entanglement survives even when one detector is untrusted. This eliminated the detection loophole that had plagued quantum optics for 40 years .
| Tool | Function | Innovation |
|---|---|---|
| Superconducting TES Arrays | Photon detection via microkelvin temperature shifts | Near-zero dark counts; 98% photon-sensitive surface |
| Periodically Poled KTP Crystals | Entangled photon pair generation | Ultra-bright sources (10⁶ pairs/sec/mW) |
| Steering Inequalities | Mathematical entanglement verification | Detects entanglement with untrusted devices |
| Monte Carlo Quantum Trajectories | Modeling nanomagnet fluctuations | Predicts quantum noise dominance at T<1K |
These tools transformed quantum verification from philosophical debate to engineering challenge. As Yong Wang described in Session Y15, quantum Monte Carlo techniques now model spin transfer torque in nanomagnets—crucial for future quantum memory—by treating electron scatterings as quantum "kicks" to magnetic coherence 8 .
The 2012 meeting's revelations catalyzed three seismic shifts:
Quantum key distribution now uses steering for hack-proof encryption, with China's Micius satellite employing TES-derived tech.
Session A17's thermoelectric nanomaterials and A26's battery innovations paved the way for room-temperature superconductivity searches.
Once philosophical, foundations became practical—today's quantum processors leverage steering for error correction.
"The universe is not only stranger than we imagine—it's stranger than we can imagine... but with the right tools, we can subpoena it to testify."
As session chair Christopher Fuchs noted, closing the detection loophole meant we could finally "take quantum weirdness to the bank." Ten years later, the 2012 APS March Meeting stands as the proving ground where quantum mechanics transitioned from paradox to protocol—one superconducting sensor at a time 6 .