- Researchers transform 20 entangled quantum bits into Schrödinger cat states.
- This breaks the old record of 14 qubits which was established in 2011.
- Such superimposed states could provide an important resource for various applications, ranging from quantum metrology to quantum computation.
In 1935, an Austrian physicists Erwin Schrödinger came up with a thought experiment — sometimes described as paradox — in which a cat is trapped in a steel chamber along with hydrocyanic acid, a hammer and a tiny amount of radioactive material.
There is a fifty percent chance that one of the atoms of the radioactive material decays and if it happens, a relay mechanism will trip the hammer, shattering a small flash of hydrocyanic acid which will eventually cause the cat to die.
The scenario presents a hypothetical cat that may be both dead or alive at the same time. You wouldn’t know if the cat was dead or alive until you opened the box.
Schrödinger used this thought experiment to explain the state known as quantum superposition, a fundamental principle of quantum mechanics. According to quantum law, atoms or photons can exist in multiple states (superpositions) that correspond to different outcomes.
Scientists have proved the existence of superposition by analyzing interference in light waves. They have carried out numerous experiments over the past four decades to realize the superposition of quantum states.
But since these cat states are intensively sensitive, even the tiniest environmental disturbance causes them to collapse. Therefore, scientists have been able to realize only a small number of quantum bits in Schrödinger cat states.
Now, an international team of researchers has transformed 20 entangled quantum bits (qubits) into Schrödinger cat states. This breaks the old record of 14 qubits which was established in 2011. The creation of such a state of superposition can be considered as a crucial step in the advancement of quantum computing.
How Did They Do This?
Unlike classical bits that can have one particular value at a time (either 1 or 0), qubits can have multiple states simultaneously due to the superposition principle. Thus, they can store and process multiple values in a single step (in parallel).
The number of quantum bits plays an important role here. With 20 qubits, for instance, there can be more than 1,000,000 superimposed states. And 300 qubits can store more than one quintillion vigintillion (1081) particles (or more than the number of atoms in the entire universe).
Reference: ScienceMag | DOI:10.1126/science.aax9743 | Forschungszentrum Jülich
To realize Schrödinger cat states With 20 qubits, researchers used a programmable quantum simulator based on arrays of Rydberg atom. In this procedure, they aligned individual atoms of rubidium side by side in a row, using laser beams (red). This method is also called optical tweezers.
Laser beams (red) capture Rubidium atoms. Another laser (blue) excites some atoms so that their shells combine with the adjacent atoms | Credit: Tobias Schlößer
They then used another laster (blue) to put atoms in a special state — Rydberg state — where electrons are situated far from the nucleus. Typically, this complex process takes too much time and superimposed states get destroyed even before they can be measured.
To solve this problem, researchers cleverly switched the lasers on and off at an optimal rate. This helped them speed up the process and make a new record.
Some atoms were inflated in such a way that their atomic shells combine with the adjacent atoms to produce two opposite configuration at the same time, namely excitations occupying all odd and even sites. And that’s how the team was able to form the superposition of opposite configuration called the Greenberger-Horne-Zeilinger state.
Such Schrödinger cat states of the Greenberger-Horne-Zeilinger type provide a crucial resource for various applications, ranging from quantum metrology and quantum networking to quantum error correction and quantum computation.