The quantum realm is notoriously full of uncertainties, but observers like us still manage to agree on how we experience it in very concrete ways. A quantum framework inspired by evolutionary principles may explain how such consensus is possible 鈥� and now researchers have proved it mathematically.
鈥淓very day, when you go outside, you see things. And you see them as localised. You don鈥檛 see weird quantum features. So, the question is, how can we connect this divide between quantum and classical?鈥� says at Los Alamos National Laboratory (LANL) in New Mexico.
A framework called quantum Darwinism could make that connection. Proposed by , also at LANL, this idea uses a process similar to natural selection to show how we end up seeing a non-quantum world and agreeing on what it is like.
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The quantum world is full of existential fuzziness: each quantum object is a cloud of possible states of being until it is measured or observed, at which point it assumes one well-defined, or 鈥渃lassical鈥�, state. Physicists have debated what mechanism underlies this transition for decades. With quantum Darwinism, Zurek suggested that the states we ultimately see are somehow more robust than the rest in the cloud of possibilities 鈥� in the language of natural selection, these states are more 鈥渇it鈥�.
When a quantum object interacts with its environment, some of its possible states are destroyed, but these special states survive by replicating themselves. Thus, when you look at an object and see it as unfuzzy, you are really seeing one in the long chain of these copies.
In their new work, Touil, Zurek and their colleagues considered how much two observers could agree on the aftermath of this process. They studied a scenario where each observer only has access to a fraction of the object鈥檚 environment and never the object itself. With such limited information, each observer could end up with a vastly different mental picture of the object.
To quantify the difference in their perceptions, the team calculated the observers鈥� 鈥渕utual information鈥�, a number that captures the overlap between what each one learns about the object. For a broad class of objects and environments of different sizes, they found that the observers reach consensus on the non-quantum world they observe.
at the Polish Academy of Sciences says this fills in a detail that had so far been missing from quantum Darwinism, which he says is a 鈥渂rilliant and necessary鈥� framework for understanding how we interact with the quantum world. 鈥淐onsider you and me are looking at something, let鈥檚 say at my glass of water,鈥� he says. 鈥淭here is a correlation between the glass of water and us seeing, and then the question is, 鈥業s there a direct correlation between me and you?鈥� This work completes that picture.鈥� Specifically, the researchers found that this correlation exists. 鈥淎lthough trivial in ordinary life, such questions are not necessarily obvious in the quantum world,鈥� he says.
In addition to mathematical calculations, Touil and his colleagues worked with researchers at Zhejiang University in China to translate their work into an experiment. It used 12 quantum bits, or qubits, inside of a quantum computer, with two of the qubits designated as the object and the remaining 10 as their environment. The researchers obtained preliminary data on how those qubits鈥� quantum states change over time 鈥� and these results were consistent with the predictions of quantum Darwinism.
Touil and at the University of Houston in Texas on 19 March at the American Physical Society Global Physics Summit in California.
Touil says this is the biggest such experiment to date, but similar studies had also offered encouraging results in the past. Such experiments strengthen the case for quantum Darwinism as an explanation for how the quantum world becomes the world that we know, says Korbicz.
at the University of Nottingham in the UK says the new work adds weight to quantum Darwinism as a way of understanding how the classical world emerges from the quantum, but there is still room for adding more detail to the framework. For instance, future calculations could pinpoint not just how much observers agree on the classical world they observe, but the exact content of their observations. And the question remains whether any trace of quantumness can survive the process of reaching consensus, he says.
Touil also wants to go beyond qubits and explore how quantum Darwinism can explain the full richness of the physical world. For example, he wants to relate his team鈥檚 work to quantum states of matter, which can be created in the lab with special materials or extremely cold atoms. In this way, quantum Darwinism may be able to explain not just why we see a non-quantum world, but also why that world still contains some examples of quantumness.
