Quantum Communication Without Exchanging Particles

A University of Bristol physicist provides the first-ever practical blueprint for creating in the lab a wormhole that verifiably bridges space, as a probe into the inner workings of the universe. It involves creating a new kind of quantum computer, investigation of quantuum physics in a new way and a possible path to some kind of wormhole science or technology.

He calls the new method ‘counterportation’. Study author Hatim Salih, Honorary Research Fellow at the university’s Quantum Engineering Technology (QET) Labs, is co-founder of the start-up DotQuantum.

“If counterportation is to be realized, an entirely new type of quantum computer has to be built: an exchange-free one, where communicating parties exchange no particles,” Hatim said.

In their conception, a local wormhole is a physical system characterized by the no-cloning of information that mediates the action of an exchange-free quantum computer: locally induced spatial entanglements of a single particle, and corresponding self-interference scenarios allow entangling other degrees of freedom among spatially separated parties, without any particle observably crossing—rendering space disjunctly traversabile.

A constructor-theoretic approach has thus enabled us to precisely characterise a local ER bridge in terms of a task/constructor pairing, namely the disjunct traversability of space by means of an exchange-free quantum computer, without assuming any specific quantum gravity dynamics. Explaining counterportation, EPR provides a dynamical account of how a local wormhole mediates qubit exchange-free interaction.

The lab demonstration requires what is essentially a two-qubit exchange-free quantum computer. By contrast to large-scale quantum computers that promise remarkable speed-ups, the promise of exchange-free quantum computers of even the smallest scale is to make seemingly impossible tasks possible by incorporating space fundamentally. Ultimately, they see exchange-free quantum computers coming into their own exploring the fundamental physics of the Universe.

Accomplishing the mission of counterporting an object across space—thereby traversing a local wormhole, as if through an extra spatial dimension—comes down to locally induced spatial entanglements of a single particle, and corresponding self-interference scenarios at work. But as Richard Feynman was quick to point out, such interference ‘has in it the heart of quantum mechanics.’ Even further, the uncovered phenomenon of counterportation provides a smoking gun for the existence of an underlying physical reality.

Researchers propose an experimental realization of the protocol for the counterfactual disembodied transport of an unknown qubit—or what we call counterportation—where sender and receiver, remarkably, exchange no particles. They employ cavity quantum electrodynamics, estimating resources for beating the classical fidelity limit—except, unlike teleportation, no pre-shared entanglement nor classical communication are required. The approach is multiple orders of magnitude more efficient in terms of physical resources than previously proposed implementation, paving the way for a demonstration using existing imperfect devices. Surprisingly, while such communication is intuitively explained in terms of ‘interaction-free’ measurement and the Zeno effect, we show that neither is necessary, with far-reaching implications in support of an underlying physical reality. They go on to characterize an explanatory framework for counterportation starting from constructor theory: local wormholes. Conversely, a counterportation experiment demonstrating the traversability of space, by means of what is essentially a two-qubit exchange-free quantum computer, can point to the existence in the lab of such traversable wormholes.

Universal exchange-free quantum computation

The exchange-free CNOT gate is the key primitive for the protocol for the counterfactual disembodied transport of an unknown qubit, counterportation.

The gate itself was the earliest counterfactual gate to be proposed, two-qubit or otherwise, and allows universal exchange-free quantum computation as a new computing paradigm. The definition of counterfactuality, with the target qubit of the gate at one subsystem, Alice, and the control qubit at another, Bob, is that the two spatially-separated subsystems exchange no particles during the computation. Bristol researchers use the circular polarisation basis as it ties better with our experimental proposal for Bob’s qubit. They provide a more succinct derivation in what follows before showing how to incorporate an improvement based on recent work by Aharonov and Vaidman, so as to establish broad agreement on counterfactuality. Aharonov and Vaidman’s improvement is therefore readily adopted as an integral part of our exchange-free gate. Consider a right-circular polarised, R, photon entering the top chained quantum Zeno effect module CQZE1 in figure 2(C).