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Schrödinger's cat has become one of the most famous examples of the bizarre behaviour of quantum mechanics.

If you put a cat inside an opaque box and make his life dependent on a random event, when does the cat die? When the random event occurs, or when you open the box?

Common sense may suggest the former, but quantum mechanics suggests someone has to observe the result before the cat is dead.

Continuous monitoring of a quantum system can direct it along a random path. This map shows how scientists tracked the transition between two states many times to determine how it changes. They found quantum particles follow the classical path of least resistance

Until that moment, the cat is both dead and alive at the same time.

Now physicists at the University of California, Berkeley, have for the first time showed that, in fact, it's possible to follow the metaphorical cat through the whole process – regardless of whether the cat lives or dies.

The researchers were able to do this by tracking the path that quantum particles, such as atoms or photons, follow.

What they saw is that quantum particles follow the classical path of least resistance – just as pedestrian paths on streets gradually emerge after new sod is laid.

Kater Murch (right), assistant professor of physics, and junior Chris Munley work with the equipment that can map a quantum device's trajectory between two points in quantum state space, a feat until recently considered impossible

Usually, when quantum particles are 'touched' by the outside world, they lose this quantum strangeness and collapse into a 'classical state'.

But in the past 20 years, physicists have devised devices that isolate quantum systems from the environment and allow them to be probed so gently that they don't immediately collapse.

With these devices, scientists can at last follow quantum systems into the bizarre and murky world of quantum territory.

'Real-time tracking of a quantum system shows that it's a continuous process, and that we can constantly extract information from the system as it goes from quantum to classical,' said Irfan Siddiqi, UC Berkeley associate professor of physics.

'This level of detail was never considered accessible by the original founders of quantum theory.'

Professor Siddiqi's experiment involved using a simple superconducting circuit that has different energy levels, or states, just like an atom.

The team used the system's lowest two energy levels, the ground state and an excited state, as their model quantum system.

Between these two states, there are an infinite number of quantum states and the device was able to probe these energy levels before they collapsed into a classical.

The quantum state of the circuit was detected by putting it inside a microwave box. A very small number of microwave photons were sent into the box where their quantum fields interacted with the superconducting circuit.

The box then provided information about the quantum system in the form of a phase shift – or the position of the troughs and peaks of something known as the photons' wavefunctions.

In Schrödinger's cat experiment, a cat in a box, whose fate is decided by subatomic particles, is both alive and dead until someone looks at it

Because even gentle probing makes each quantum trajectory noisy, the team repeated the experiment a million times and examined which paths were most common.

'But real-time tracking of a quantum system shows that it's a continuous process, and that we can constantly extract information from the system as it goes from quantum to classical,' said Professor Siddiqi.

For quantum computers, this would allow continuous error correction.

'The implications are significant, as now we can design control sequences to steer a system along a certain trajectory,' said Professor Siddiqi.

'For example, in chemistry one could use this to prefer certain products of a reaction over others.'

Chemistry at its most basic level is described by quantum mechanics.

In the past 20 years, chemists have developed a technique called quantum control, where shaped laser pulses are used to drive chemical reactions.

'The chemists control the quantum field from the laser, and that field controls the dynamics of a reaction,' explained Kater Murch, PhD, an assistant professor of physics at Washington University.

'Eventually, we'll be able to control the dynamics of chemical reactions with lasers instead of just mixing reactant one with reactant two and letting the reaction evolve on its own,' he said.