シュレディンガーの猫の実験は物理学者の記録を破った

スイス連邦工科大学チューリッヒ校の研究者は、水晶を 2 つの振動状態の重ね合わせに配置することにより、これまでで最も重いシュレディンガーの猫を作成しました。 彼らの結果は、より強力なキュービットにつながり、キュービットが日常生活で観察されない理由を説明するのに役立つ可能性があります。

• ETHチューリッヒの研究者は、シュレディンガーの最も重い猫をこれまでに作成しました.
• このために、彼らは発振結晶と超伝導回路を組み合わせました。
• 彼らは、巨視的な世界で量子効果が消える理由をよりよく理解したいと考えています。

量子物理学者でなくても、シュレディンガーの有名な猫のことは聞いたことがあるでしょう。 Erwin Schrödinger は、1935 年の思考実験で、生きている猫と死んでいる猫を同時に考え出しました。明らかなパラドックスです。結局のところ、日常生活では、生きているか生きている猫しか見ません。 また 死んだ – 科学者は実験室で同様の状況を実現しようとしました。 これまでに、例えば、原子や分子を量子力学的な重ね合わせ状態で同時に 2 か所に存在させることで、これを行うことができました。

ETH では、固体物理学研究所の教授である Yiwen Chu が率いる研究チームが、小さな結晶を 2 つの振動状態の重ね合わせに配置することにより、劇的に重いシュレディンガーの猫を作成しました。 彼らの結果は今週、科学雑誌 Science に掲載され、より強力なキュービットにつながり、巨視的な世界で量子重ね合わせが観察されない理由の謎に光を当てる可能性があります。

箱入り猫

シュレーディンガーの最初の思考実験では、放射性物質、ガイガー カウンター、毒の入った小瓶が入った金属製の箱の中に猫が閉じ込められています。 特定の時間枠 (たとえば 1 時間) で[{” attribute=””>atom in the substance may or may not decay through a quantum mechanical process with a certain probability, and the decay products might cause the Geiger counter to go off and trigger a mechanism that smashes the flask containing the poison, which would eventually kill the cat. Since an outside observer cannot know whether an atom has actually decayed, he or she also doesn’t know whether the cat is alive or dead – according to quantum mechanics, which governs the decay of the atom, it should be in an alive/dead superposition state. (Schrödinger’s idea is commemorated by a life-​size cat figure outside his former home at Huttenstrasse 9 in Zurich).

In the ETH Zurich experiment, the cat is represented by oscillations in a crystal (top and blow-​up on the left), whereas the decaying atom is emulated by a superconducting circuit (bottom) coupled to the crystal. Credit: Yiwen Chu / ETH Zurich

“Of course, in the lab we can’t realize such an experiment with an actual cat weighing several kilograms,” says Chu. Instead, she and her co-​workers managed to create a so-​called cat state using an oscillating crystal, which represents the cat, with a superconducting circuit representing the original atom. That circuit is essentially a quantum bit or qubit that can take on the logical states “0” or “1” or a superposition of both states, “0+1”. The link between the qubit and the crystal “cat” is not a Geiger counter and poison, but rather a layer of piezoelectric material that creates an electric field when the crystal changes shape while oscillating. That electric field can be coupled to the electric field of the qubit, and hence the superposition state of the qubit can be transferred to the crystal.

Simultaneous oscillations in opposite directions

As a result, the crystal can now oscillate in two directions at the same time – up/down and down/up, for instance. Those two directions represent the “alive” or “dead” states of the cat. “By putting the two oscillation states of the crystal in a superposition, we have effectively created a Schrödinger cat weighing 16 micrograms,” explains Chu. That is roughly the mass of a fine grain of sand and nowhere near that of a cat, but still several billion times heavier than an atom or molecule, making it the fattest quantum cat to date.

In order for the oscillation states to be true cat states, it is important that they be macroscopically distinguishable. This means that the separation of the “up” and “down” states should be larger than any thermal or quantum fluctuations of the positions of the atoms inside the crystal. Chu and her colleagues checked this by measuring the spatial separation of the two states using the superconducting qubit. Even though the measured separation was only a billionth of a billionth of a meter – smaller than an atom, in fact – it was large enough to clearly distinguish the states.

Measuring small disturbances with cat states

In the future, Chu would like to push the mass limits of her crystal cats even further. “This is interesting because it will allow us to better understand the reason behind the disappearance of quantum effects in the macroscopic world of real cats,” she says. Beyond this rather academic interest, there are also potential applications in quantum technologies. For instance, quantum information stored in qubits could be made more robust by using cat states made up of a huge number of atoms in a crystal rather than relying on single atoms or ions, as is currently done. Also, the extreme sensitivity of massive objects in superposition states to external noise could be exploited for precise measurements of tiny disturbances such as gravitational waves or for detecting dark matter.

Reference: “Schrödinger cat states of a 16-microgram mechanical oscillator” by Marius Bild, Matteo Fadel, Yu Yang, Uwe von Lüpke, Phillip Martin, Alessandro Bruno and Yiwen Chu, 20 April 2023, Science.
DOI: 10.1126/science.adf7553