양자 어닐러, Annealer, 우주의 종말

과학자들이 양자컴퓨팅 기술로 우주의 종말을 예측하는 물리학 이론을 시뮬레이션하는 데 성공했다.

즐라트코 파픽 영국 리즈대 물리천문학부 교수와 자카 보뎁 독일 율리히 물리학연구소 연구원 공동 연구팀은 양자컴퓨팅 원리를 활용해 우주의 궁극적인 변화를 예측하는 시뮬레이션을 수행하고 연구 결과를 국제학술지 '네이처 피직스'에 공개했다.

현대물리학의 핵심 이론 중 하나인 양자장 이론에 따르면 우주는 빅뱅 이후 냉각돼 '가짜 진공(False vacuum)' 상태에 있다. 진공은 에너지 수준이 국소적으로 최솟값을 갖는 상태를 말한다. 가짜 진공은 에너지 수준이 더 낮은 상태인 '진짜 진공(True vacuum)'으로 붕괴될 수 있다.

홍성욱 한국천문연구원 책임연구원은 "우주가 가짜 진공 상태에 있다면 언젠가 진짜 진공으로 바뀔 수 있다는 것"이라며 "진짜 진공으로 변하면 원래의 가짜 진공 우주는 종말한다고 볼 수 있다"고 설명했다. 지금은 안정적인 것처럼 보이는 우주가 언젠가 붕괴해 '종말'에 이른다는 뜻이다. 실제로 종말에 이르기까지는 천문학적인 시간이 걸릴 것으로 추정된다.

그간 가짜 진공이 붕괴하는 징후를 찾으려는 시도가 꾸준히 있었지만 쉽지 않았다. 가짜 진공 상태를 설명하려면 여러 입자 사이의 상호작용을 계산해야 한다. 이때 입자의 수가 조금만 늘어도 계산이 기하급수적으로 복잡해져 기존 알고리즘으로는 해결이 어려웠다.

연구팀은 캐나다 양자컴퓨팅 기업 디웨이브 퀀텀의 양자 어닐러(Annealer)를 활용했다. 양자 어닐러는 범용성은 없지만 최적화 문제를 풀기 위해 특화된 양자컴퓨팅이다. 홍 책임연구원은 "거짓 진공 문제는 양자역학 문제에 해당하기 때문에 양자역학 자체를 계산에 활용하는 양자컴퓨팅으로 풀어내기 용이한 것"이라고 설명했다.

연구팀은 5564큐비트(qubit)급 양자 어닐러를 활용해 가짜 진공 상태에서 진짜 진공이 생겨나는 '우주 거품'을 시뮬레이션했다. 큐비트는 양자컴퓨팅의 정보처리 단위다. 가짜 진공 우주가 진짜 진공으로 바뀌는 부분은 밖에서 관찰할 때 마치 거품처럼 묘사된다.

연구팀은 가짜 진공 붕괴로 우주 거품이 형성되는 과정과 거품 사이의 상호작용을 시뮬레이션으로 관찰하는 데 성공했다. 양자컴퓨팅이 새로운 물리학 실험 도구가 된 것이다.

 

 

 

 

Scientists have succeeded in simulating a physics theory that predicts the end of the universe with quantum computing technology.

Zlatko Papik, a professor of physics and astronomy at Leeds University in the UK, and a joint research team at the Jülich Institute of Physics in Germany, Xhaka Bodeb, conducted simulations to predict the ultimate change in the universe using quantum computing principles and published the research results in the international journal Nature Physics.

According to quantum field theory, one of the core theories of modern physics, the universe is in a "false vacuum" state after the Big Bang. Vacuum refers to a state in which the energy level has a local minimum. A fake vacuum can collapse into a "true vacuum" in which the energy level is lower.


"If the universe is in a fake vacuum, it can turn into a real vacuum someday," said Hong Seong-wook, a senior researcher at the Korea Astronomy and Space Science Institute. "If it turns into a real vacuum, it can be said that the original fake vacuum will end." This means that the universe, which seems to be stable now, will collapse one day to reach the end. It is estimated that it will take astronomical time before it actually ends.

There have been steadily attempts to find signs of the fake vacuum collapsing, but it has not been easy. To explain the fake vacuum state, the interaction between several particles must be calculated. At this time, even a small increase in the number of particles made the calculation exponentially complicated, making it difficult to solve with existing algorithms.

The research team used quantum annealer from D-Wave Quantum, a Canadian quantum computing company. Quantum annealer is not universal but specialized quantum computing to solve optimization problems. "Since a false vacuum problem corresponds to a quantum mechanics problem, it is easy to solve it with quantum computing that uses quantum mechanics itself for calculation," said Hong.

The research team used a 5564-qubit quantum annealer to simulate a "space bubble" in which a real vacuum is created in a fake vacuum. A qubit is an information processing unit of quantum computing. The part where a fake vacuum turns into a real vacuum is depicted as a bubble when viewed from the outside.

The research team succeeded in simulating the interaction between the formation of space bubbles by fake vacuum decay. Quantum computing has become a new physics experimental tool.