## Archived Articles

**Uncertainty and nonlocality**: a description of my paper with Stephanie Wehner, Science 2010.**Quantum information can be negative**: an accessible description of my paper with Horodecki and Winter in Nature.**Sending quantum information down channels which cannot convey quantum information**: A perspective in Science. A copy is available here.**Quantum computing as free falling**: A Science perspective on quantum computation as geometry. A copy is available here.

## Research Interests

I'm currently very engaged in using insights from quantum informatin theory to probe fundamental physics. This effort spans several fields, including quantum information theory, reconciling quantum mechanics and gravity, black hole thermodynamics, and the foundations of quantum theory. Although these fields are often distinct, there are many conceptual overlaps, as can be seen below. You can check out my google scholar page here.## Selected publications

- J. Oppenheim, Carlo Sparaciari, Barbara Soda, Zach Weller-Davies Gravitationally induced decoherence vs space-time diffusion: testing the quantum nature of gravity (2023)
- J. Oppenheim A postquantum theory of classical gravity (2023)
- L. Masanes and J. Oppenheim, " A derivation (and quantification) of the third law of thermodynamics" (2017)
- M. Horodecki and J. Oppenheim, "Fundamental limitations for quantum and nano thermodynamics", Nature Communications 4, 2059 (2013)
- J. Oppenheim and S. Wehner, "The Uncertainty Principle Determines the Nonlocality of Quantum Mechanics", Science 330:1072-1074 (2010)
- M. Horodecki, J. Oppenheim, A. Winter, "Partial quantum information", Nature 436:673-676 (2005)
- K. Horodecki, M.Horodecki, P. Horodecki, J. Oppenheim, "Secure key from bound entanglement", Phys. Rev. Lett. 94, 160502 (2005)

## A postquantum theory with classical spacetime

*"The hardest thing of all is to find a black cat in a dark room, especiall if there is no cat."*

Reconciling quantum mechanics with General Relativity (Einstein's theory of gravity), is one of the grand challenges of modern physics. Rather than attempting to quantise gravity, my latest research takes a different approach -- I have instead been developing a consistent theory of quantum field theory coupled to classical spacetime. I've set out why I believe it's reasonable to question whether we should quantise the spacetime metric here, and the proposal can be found in "postquantum theory of classical gravity" based on a master equation approach. With Zach Weller-Davies, we now have a path integral formulation of it. The theory is formally renormalisable, which is exciting, since it allows us to think of gravity as a theory of spacetime down to the shortest of distances.

These theories do not need the measurement postulate of quantum mechanics as the Born rule follows from the dynamics. These results follow from the derivation of the most general form of evolution laws for classical systems coupled to quantum ones in 1811.03116 and 2203.01332. We have proposed an experiment, to test whether spacetime is classical via something we call, the decoherence vs diffusion trade-off. Consistent coupling of quantum fields to classical spacetime ncessarily requires the metric to have stochastic fluctuations. If these fluctuations are strong enough, they could provide an alternative explaination to the phenomena we currently regard as dark matter (see here and here).

## Quantum information theory

*"You don't understand quantum mechanics, you just get used to it."*

-- attributed to Feynman, borrowed from von Neumann.

-- attributed to Feynman, borrowed from von Neumann.

Quantum information theory is currently a very exciting field, and we are constantly learning new and surprising things about quantum mechanics. I am interested in quantum communication theory, quantum cryptography, and entanglement manipulation.

Much of my work is in understanding the basic blocks of quantum information theory -- what does it mean for one quantum system to have information about another system. This is often best understood through communication theory. If an individual has a lot of information about my system, then I don't need to send them many qubits for them to possess the rest of my state. It was this idea which led to state merging and negative information.

## Quantum Thermodynamics

*"In this house, young lady, we obey the laws of thermodynamics!" --Homer Simpson*

The laws of thermodynamics govern much of the world around us. They tell us that a hot cup of tea in a cold room will cool down rather than heat up; they tell us that unless we are vigilant, our houses will become untidy rather than spontaneously tidy; they tell us how efficient the best heat engines can be. But the laws of thermodynamics only apply to large objects, when many particles are involved. Can the laws of thermodynamics be applied to small systems, such as the kind of microscopic motors currently been fabricated in labs? Or perhaps even quantum systems? Surprisingly, the answer is yes. I'm interested in formulating laws of thermodynamics for quantum systems. We find for example, that at the small scale, there are many second laws, not just one, and that we can formulate a stronger version of the zeroth law which helps us to naturally define the notion of temperature. This builds on some of my previous work deriving thermo-majorisation criteria, which was proven to be necessary and sufficient for thermodynamical state transformations.

## Foundations of quantum mechanics

*"It is very difficult to be more interesting than quantum mechanics."*

--Gaspar, to the frustrated wife of a physicist (who shall remain anonymous)

--Gaspar, to the frustrated wife of a physicist (who shall remain anonymous)

As a general rule, I am interested in understanding how one might be able to generalize our current laws of evolution and the state space these laws act on. This is not only to understand what other laws might be possible, but also to understand what is so special about current physical laws and states. Other areas of interest, include for example, probabilistic interpretations of unitaries. In quantum mechanics, outcomes of measurements on a state have a probabilistic interpretation while the evolution of the state is treated deterministically. However, it turns out that one can also treat the evolution as being probabilistic in nature and one can measure `which evolution' happened.

I am also interested in the role of time in quantum mechanics, which was the subject of my Ph.D thesis. There, it was proposed that there is a new fundamental limitation on the accuracy of measurements of the time of an event. It is also impossible to tell the past from the future