Two University of Toronto quantum physicists, Jeff Lundeen and Aephraim Steinberg, say they have shown that Hardy's paradox(1), a proposal that has confounded physicists and science journalists trying to explain it since the 1990s, can be both confirmed and resolved. So take one more quantum problem out of the realm of 'impossible.'
Hardy's Paradox explained (poorly) is that when a positron, antiparticle of an electron, and an electron go through the interferometers (see image below) simultaneusly, the two particles should meet in an "annihilation area" and destroy one another, but Hardy showed something else: quantum theory predicts that both particle and antiparticle could disturb, yet fail to annihilate, each other in the overlapping arms. Why? Because in the quantum world they can be both in and not in the overlapping arms.
"For nearly a century, the widespread interpretation of quantum mechanics suggests that everything is uncertain until it is observed, and that observation inevitably alters reality," says Professor Steinberg. "However, in the 1990s, a technique known as 'interaction-free measurement' seemed to promise the ability to 'see without looking,' as a Scientific American article put it at the time. But when Lucien Hardy proposed that one could never reliably make inferences about past events which hadn't been directly observed, a paradox emerged which suggested that whenever one attempted to reason about the past in this way they would be led into error."
Over the course of nearly two years of work, Steinberg and then-student Jeff Lundeen, now a research associate at the National Research Council of Canada, built a complicated quantum optical experiment and developed new theoretical tools.
Thanks to the multiple existences of particles, they can simultaneously be in and yet not in the overlapping arms. Quantum theory allows an improbable yet entirely possible outcome that makes no sense. This is Hardy's paradox.
In essence, they combined Hardy's Paradox with a new theory known as weak measurement proposed by Tel Aviv University physicist Yakir Aharonov(2), showing that in one sense, one can indeed talk about the past, resolving the paradox. Weak measurement is a tool whereby the presence of a detector is less than the level of uncertainty around what is being measured, so that there is an imperceptible impact on the experiment.
"We found that all of the seemingly paradoxical conclusions in Hardy's Paradox can, in fact, be experimentally verified," says Steinberg, "but that the use of weak measurement removes the contradiction."
"Until recently, it seemed impossible to carry out Hardy's proposal in practice, let alone to confirm or resolve the paradox," he says. "We have finally been able to do so, and to apply Aharonov's methods to the problem, showing that there is a way, even in quantum mechanics, in which one can quite consistently discuss past events even after they are over and done. Weak measurement finds what is there without disturbing it."
Article: J. S. Lundeen, A. M. Steinberg, 'Experimental Joint Weak Measurement on a Photon Pair as a Probe of Hardy's Paradox', Phys. Rev. Lett. 102, 020404 (2009) DOI:10.1103/PhysRevLett.102.020404
(1) Boschi, D, S Branca, F de Martini and L Hardy, “Ladder Proof of Nonlocality without Inequalities: Theoretical and Experimental Results”, Physical Review Letters 79, 2755 (1997)
(2) Yakir Aharonov, Alonso Boteroc, Sandu Popescu,Benni Reznika, Jeff Tollaksen, 'Revisiting Hardy's paradox: counterfactual statements, real measurements, entanglement and weak values', Physics Letters A Volume 301, Issues 3-4, 26 August 2002, Pages 130-138, doi:10.1016/S0375-9601(02)00986-6
- PHYSICAL SCIENCES
- EARTH SCIENCES
- LIFE SCIENCES
- SOCIAL SCIENCES
Subscribe to the newsletter
Stay in touch with the scientific world!
Know Science And Want To Write?
- Top Secret: On Confidentiality On Scientific Issues, Across The Ring And Across The Bedroom
- The Mystery Of The Red Sea
- Stop Using BMI To Determine Health
- Would New Planet X Clear Its Orbit? - And Any Better Name Than "Planet Nine"?
- The Greenhouse Effect Fallacy
- Intense Work Helped Michelangelo Maintain Use Of Hands Despite Osteoarthritis
- Skyscraper Tall Telescope For Hawaii Mountain - Should Astronomers Build It?
- "Greetings Robert. Thanks again for your thoughts on God. I read your two statements and here are..."
- "Hello Vance,yes I know about that model, and about at least two experimental attempts, one with..."
- "No, I am not from the states. It sounds like an astonishing arrangement to have multiple jurisdiction..."
- "Very true. The observation I've made is that in 2001 it was John F. Nash and Alicia DeLarde ..."
- "The male female difference you think is so basic isn't so simple. Consider this bird. http..."
- BMI is Bologna
- Energy Drinks: The Dose Makes the Poison
- California’s Prop 65: Bad For Public Acceptance Of Science, About To Get Worse
- Wear Red Today! It’s Women’s Heart Health Awareness Day
- Can Marijuana Ease NFL Players’ Pain? Claims Are All Over The Field
- Mid-Life Crisis Clusters Found In 4 US Cities
- Cambridge researcher develops smartphone app to map Swiss-German dialects
- Studies link healthy workforces to positive stock market performance
- Pioneering discovery leads to potential preventive treatment for sudden cardiac death
- Online shopping might not be as green as we thought
- Gene family turns cancer cells into aggressive stem cells that keep growing