22 May 2018
  • Research Result

Using geometry and qubits to build real universes

New Kyoto University tool connects spacetime and quantum mechanics

Kyoto, Japan -- Researchers at Kyoto University's Yukawa Institute for Theoretical Physics have announced the discovery of a new geometric formula for computing an amount of quantum information of quantum bits.

The conjecture, published in Nature Physics established by Koji Umemoto and Tadashi Takayanagi, can be regarded as a generalization of the black hole entropy formula -- "Bekenstein-Hawking" formula -- providing a new tool for studying the deep connections between gravity and the quantum realm.

In physics, quantum mechanics explains the basic laws of micro-phenomena. The smallest discrete unit of information of this scale is called a quantum bit, or qubit. Recently, scientists have been actively exploring new conjectures to link quantum mechanics with general relativity, with projects such as 'It from Qubit' facilitating this inquiry.

String theory is a promising framework unifying the two principles, with theorists working to show how universes with gravity can emerge from quantum bits.

The team conducted geometrical calculations in gauge/gravity correspondence to derive various properties that match quantum values. The properties were then confirmed to precisely agree with known values in quantum information theory.

The final published formula shows that an amount of information shared by two objects A and B -- especially in mixed states, called "entanglement of purification" -- is equal to the cross-sectional area of a tunnel connecting the two in a gravitational universe.

Takayanagi states that to understand the origins of the universe, researchers must comprehend the basic laws of micro-universes -- ie a quantum theory of gravity. Deriving the fundamentals of spacetime from quantum bits provides a crucial step toward achieving that goal.

The team intends to further explore the deep connections between gravity and quantum information, as their formula is only the gateway to a new region of inquiry.


Researchers find develop a formula that explores the connection between gravity and the quantum world (GiroScience -

Paper information


Koji Umemoto & Tadashi Takayanagi (2018). Entanglement of purification through holographic duality. Nature Physics.