What role does quantum mechanics play in the machinery of life? Nobody is quite sure, but in recent years, physicists have begun to investigate all kinds of possibilities. In the process, they have gathered evidence suggesting that quantum mechanics plays an important role in photosynthesis, in bird navigation, and perhaps in our sense of smell.
There is even a speculative line of thought that quantum processes must have governed the origin of life itself and the formulation of the genetic code. The work to study these questions is ongoing and involves careful observation of the molecules of life.
But there is another way to approach this question from the bottom up. Computer scientists have long toyed with artificial life forms built from computer code. This code lives in a silicon-based landscape where its fitness is measured against some selection criteria.
It reproduces by combining with other code or by the mutation of its own code. And the fittest code has more offspring while the least fit dies away. In other words, the code evolves. Computer scientists have used this approach to study various aspects of life, evolution, and the emergence of complexity.
This is an entirely classical process following ordinary Newtonian steps, one after the other. The real world, on the other hand, includes quantum mechanics and the strange phenomena that it allows. Thatâs how the question arises of whether quantum mechanics can play a role in evolution and even in the origin of life itself.
So an important first step is to reproduce this process of evolution in the quantum world, creating artificial quantum life forms. But is this possible?
Today we get an answer thanks to the work of Unai Alvarez-Rodriguez and a few pals at the University of the Basque Country in Spain. These guys have created a quantum version of artificial life for the first time. And they say their results are the first examples of quantum evolution that allows physicists to explore the way complexity emerges in the quantum world.
The experiment is simple in principle. The team think of quantum life as consisting of two partsâa genotype and a phenotype. Just as with carbon-based life, the quantum genotype contains the quantum information that describes the individualâits genetic code. The genotype is the part of the quantum life unit that is transmitted from one generation to the next.
The phenotype, on the other hand, is the manifestation of the genotype that interacts with the real worldâthe âbodyâ of the individual. âThis state, together with the information it encodes, is degraded during the lifetime of the individual,â say Alvarez-Rodriguez and co.
So each unit of quantum life consists of two qubitsâone representing the genotype and the other the phenotype. âThe goal is to reproduce the characteristic processes of Darwinian evolution, adapted to the language of quantum algorithms and quantum computing,â say the team.
The first step in the evolutionary process is reproduction. Alvarez-Rodriguez and co do this using the process of entanglement, which allows the transmission of quantum states from one object to another. In this case, they entangle the genotype qubit with a blank state, and then transfer its quantum information.
The next stage is survival, which depends on the phenotype. Alvarez-Rodriguez and co do this by transfering an aspect of the genotype state to another blank state, which becomes the phenotype. The phenotype then interacts with the environment and eventually dissipates.
This process is equivalent to aging and dying, and the time it takes depends on the genotype. Those that live longer are implicitly better suited to their environment and are preferentially reproduced in the next generation.
There is another important aspect of evolutionâhow individuals differ from each other. In ordinary evolution, variation occurs in two ways. The first is through sexual recombination, where the genotype from two individuals combines. The second is by mutation, where random changes occur in the genotype during the reproductive process.
Alvarez-Rodriguez and co employ this second type of variation in their quantum world. When the quantum information is transferred from one generation to the next, the team introduce a random changeâin this case a rotation of the quantum state. And this, in turn, determines the phenotype and how it interacts with its environment.
So thatâs the theory. The experiment itself is tricky because quantum computers are still in their infancy. Nevertheless, Alvarez-Rodriguez and co have made use of the IBM QX, a superconducting quantum computer at IBMâs T.J. Watson Laboratories that the company has made publicly accessible via the cloud. The company claims that some 40,000 individuals have signed up to use the service and have together run some 275,000 quantum algorithms through the device.
Alvarez-Rodriguez and co used the five-qubit version of the machine, which runs quantum algorithms that allow two-qubit interactions. However, the system imposes some limitations on the process of evolution that the team want to run. For example, it does not allow the variations introduced during the reproductive process to be random.
Instead, the team run the experiment several times, introducing a different known rotation in each run, and then look at the results together. In total, they run the experiment thousands of times to get a good sense of the outcomes.
In general, the results match the theoretical predictions with high fidelity. âThe experiments reproduce the characteristic properties of the sought quantum natural selection scenario,â say Alvarez-Rodriguez and co.
And the team say that the mutations have an important impact on the outcomes: â[They] significantly improved the fidelity of the quantum algorithm outcome.â Thatâs not so different from the classical world, where mutations help species adapt to changing environments.
Of course, there are important caveats. The limitations of IBMâs quantum computer raise important questions about whether the team has really simulated evolution. But these issues should be ironed out in the near future.
All this work is the result of the teamâs long focus on quantum life. Back in 2015, we reported on the teamâs work in simulating quantum life on a classical computer. Now they have taken the first step in testing these ideas on a real quantum computer.
And the future looks bright. Quantum computer technology is advancing rapidly, which this should allow Alvarez-Rodriguez and co to create quantum life in more complex environments. IBM, for example, has a 20-qubit processor online and is testing a 50-qubit version.
That will make possible a variety of new experiments on quantum life. The most obvious will include the ability for quantum life forms to interact with each other and perhaps reproduce by sexual recombinationâin other words, by combining elements of their genotypes. Another possibility will be to allow the quantum life forms to move and see how this influences their interactions and fitness for survival.
Just what will emerge isnât clear. But Alvarez-Rodriguez and co hope their quantum life forms will become important models for exploring the emergence of complexity in the quantum world.
Eventually, that should feed into our understanding of the role of quantum processes in carbon-based life forms and the origin of life itself. The ensuing debate will be fascinating to watch.
Ref: arxiv.org/abs/1711.09442 : Quantum Artificial Life in an IBM Quantum Computer