Quantum Research

Quantum Computing, Quantum Research

Saving Schrödinger’s Cat: Researchers Discover an Early Warning Signal for Quantum Jumps


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Feature image via Science X.

Gabriella Skoff

Schrödinger’s cat is a thought experiment that has become well known as a symbol for the “weirdness” and unpredictability of the phenomenon of quantum superposition. The eponymous thought experiment devised by Austrian physicist Erwin Schrödinger in 1935 involves a cat, a vial of poison, a radioactive substance and a sealed box. The experiment dictates that if an atom of the radioactive substance decays then it will trigger the release of the poison, killing the cat; however, that may or may not happen. One can only find out if this has occurred, and therefore if the cat is alive or dead, by opening the box to observe the state of being of the cat. According to the Copenhagen Interpretation of quantum physics, until the observer peeks inside the box, the cat is actually both dead and alive. It is only when the state of the cat is observed, therefore, that the quantum superposition collapses into one or the other states and the cat is found to be either dead or alive.

Based on Niels Bohr’s 1913 proposal of quantum jumps, it was thought that the process of the cat collapsing into a theoretically dead or alive state upon observation was both instantaneous and unpredictable. However, new experimental research performed by a team of Yale researchers and published last week in Nature journal, suggests otherwise. Dr Zlatko Minev and his team’s findings conclude that a quantum jump does not actually exhibit the random, abruptness that defines the fate of Schrödinger’s cat. Rather, their research suggests, “the evolution of each [quantum] jump is continuous, coherent and deterministic”.

Within the context of Schrödinger’s cat paradox, these findings imply that the continued-life/death of the cat is simply the final stage of a process rather than an instant occurrence without foreshadowing. Further, the Yale team has detected “an advance warning signal” which indicates that a jump is about to occur. This seems to signify that we can not only detect when a quantum jump will occur but that we can also potentially reverse it during the transition. These new findings not only impact our theoretical ability to potentially save Schrödinger’s cat from its proverbial death but also have a fundamental impact in applied quantum computing.

The conundrum of a quantum jump has long presented a challenge in the applied field of quantum computing, where a jump in qubits manifest as an error in calculations. Researchers are hopeful that these new findings could potentially facilitate major advances in understanding and controlling quantum information. They anticipate that this new discovery will help to develop an early warning system that can predict when a jump, and therefore a computational error, is about to occur in order to catch it before it happens and reverse its course. While it would be a wonderful conclusion that Schrödinger’s dear cat could be saved, the real value of this research lies in its applied context: the potential to develop an advanced monitoring, detection and correction function for quantum systems, which could help bring us one step closer to a quantum advantage.

 

 

Quantum Research

The Quantum Question of an Objective Reality


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Rick and Morty explore the multiverse, a spin on the Many Worlds Interpretation.
Image via Adult Swim

Gabriella Skoff

Thought experiments in the domain of quantum physics have long captured the public imagination with their strange and “spooky” nature. Schrödinger’s at once dead-and-alive cat and its lesser-known extension, Eugene Wigner’s eponymous Wigner’s Friend, are two famous thought experiments which examine the concept of superposition and the role of the observer in quantum interactions. Until very recently, quantum technologies were simply not advanced enough to replicate Wigner’s Friend and an experiment modelled on Schrödinger’s Cat would no doubt raise serious ethical concerns for animal rights. As such, since their inception these thought experiments have been relegated to the realm of theory and imagination.

That changed last week, when Massimiliano Proietti and his team at Heriot-Watt University in Edinburgh succeeded in performing an experiment modelled on the Wigner’s friend scenario in a laboratory setting. Through this experiment, the researchers sought to explore what is known as the measurement problem—the question of how, and if, the wave function collapse occurs—the central problem in quantum mechanical interpretations.

Using the groundwork previously laid by researchers from the University of Vienna in Austria, the Edinburgh team carried out an extension of the Wigner’s Friend scenario using a “state-of-the-art 6 photon experiment”. The researchers used six entangled photons to simulate a scenario in which the role of both Wigner and his friend were occupied by measuring equipment instead of scientists. As in the thought experiment: “Wigner’s friend measures the polarization of a photon and stores the result. Wigner then performs an interference measurement to determine if the measurement and the photon are in a superposition.”

The experimental setup, as depicted by the researchers. image via
arxiv.org/abs/1902.05080 

The as yet unpublished results prove Wigner’s theory correct. The researcher’s findings suggest that two observers of a quantum interaction can observe two different realities, which are both equally real and correct simultaneously, even if they contradict each other. The implication of this assertion is that in quantum physics there is no objective reality; that reality itself is observer-dependent. The authors of the study suggest that these results necessitate an evolution in our understanding of quantum theory, a shift toward theoretical frameworks that are observer-dependent and away from interpretations that are not.

The impact of this conclusion, which proposes an unconventional interpretation of the notion of reality, could extend far beyond the discipline of physics.

Strikingly, the assumption that multiple, contradictory realities can coexist calls the concept of objective fact—the very pursuit of science itself—into question. This point, posed in an article by the MIT Tech Review, jeopardizes the assumption of the existence of “universal facts”. How might an understanding of the world around us, in which there is no shared, objective reality, change not just science but also social theory?

Of course, it is hasty to argue that quantum theory applies seamlessly to the social world, suggesting there is a direct, logical mapping. Thus far, the topic of how the microscopic quantum world effects our macroscopic, visible world has not been fully explored through research. That does not mean, however, that there is no symmetry. The question of the universality of quantum theory continues to permeate thinking today, much as it had captured the imagination of quantum theorists in the early 1900’s.

Schrödinger’s Cat (1935), for example, explores the question of the relationship between quantum and classical reality. Among other revelations, this thought experiment suggests that projecting nanoscale quantum theory onto a macro-scale experiment produces logic-defying results, ultimately leading to the conclusion that a cat cannot be both alive and dead at the same time. Schrödinger wished to argue that the dominant Copenhagen Interpretation of quantum physics, which states that an object in a state of quantum superimposition can exist in all possible configurations, does not hold at the macroscale.

Nevertheless, this problem posed by the Copenhagen Interpretation, considered by Schrödinger to be settled by his theoretical experiment, persists.

The findings of the Edinburgh team suggest that in fact Schrödinger’s cat can be both dead and alive at the same time, leading to a whole new set of questions and theories. One way to accommodate for the experiment’s result, the authors write: “…is by proclaiming that “facts of the world” can only be established by a privileged observer—e.g., one that would have access to the “global wavefunction” in the many worlds interpretation or Bohmian mechanics.”

As the authors suggest, this research potentially validates the Many-Worlds Interpretation (MWI). The MWI, as the name suggests, stipulates that each quantum interaction produces not just one result but all possible results, which exist simultaneous, branching off to form different versions of reality and producing many independent histories, futures and worlds. The researchers propose that in order for the concept of objective reality to function in the context of their findings, the holder of that knowledge must, in a godlike fashion, have access to all information from every possible reality.

Scientific theory produces claims at knowing and understanding the world around us as it really is. Quantum physics, however, has the potential to unravel this by posing the most fundamental question of all: What is reality?