Japanese researcher Makoto Kasu of Saga University and a manufacturer of precision diamond jewelry have built a 2-inch diamond-coated wafer that they claim can store 25 exabytes of data using memory quantum.

Binary data is stored in quantum overlays using nitrogen vacancies in the diamond material. Currently, the stored binary is stored as bits, with a value of one or zero, represented by magnetic polarity (north or south), flash charge (current flows or not), or resistance in ReRAM (high or low). Quantum memory is different in that it stores qubits (quantum bits).

As we understand it, a qubit can have a value of ⎢0⟩ or ⎢1⟩ (pronounced “ket 0” and “ket 1”) or a linear combination of the two states in any proportion – it doesn’t have a single value. It has a certain probability of being a ⎢0⟩ and another probability of being a ⎢1⟩. This property of a qubit is called superposition and is used in quantum computing, which can make use of other quantum phenomena such as entanglement and interference.

any number *not* of qubits equals 2^{not} parts. Ten qubits equal 2^{ten} bits or 1024 bits. Twenty qubits equals 1,048,576 bits – the information density of qubits on the scale of their numbers is staggering.

A detailed explanation of quantum computing is well beyond the scope of this article. Suffice it to say that it is based on the laws of quantum mechanics. In turn, quantum mechanics describes the properties of atoms and subatomic particles that can behave both like particles and like waves. This causes problems when measuring their properties, since the act of measurement can influence the resulting value.

IBM, Google and others are developing quantum computers, which use quantum mechanical properties to solve certain problems – those with very complex relationships between data elements. Quantum computers can solve these problems much, much faster – exponentially faster – than classical or Von Neumann computers – today’s servers and supercomputers. And they need quantum memory to do that, which is hard to achieve because the material has to behave consistently and store esoteric quantum mechanical phenomena.

This is where Makoto Kasu and Adamant Namiki Precision Jewel Co come in. They have teamed up to develop and manufacture ultra-high purity diamond slices, called Kenzan diamonds, which can function as quantum memory.

They have an artificial attribute called a nitrogen vacancy or NV center. One of the diamond’s carbon atoms is changed to a nitrogen atom. This leaves a space filled with six electrons that are in an ambiguous quantum state. The amount of nitrogen is less than three parts per billion – any more and the quantum memory functionality of the wafer is compromised.

Previously, these diamonds could only be grown in 0.006 square inch (4 mm) slices.^{2}) using a plane support. Bigger and they cracked due to internal stresses. The new development grows the diamond crystal on a stepped wafer substrate base to reduce internal stresses and achieve a circular wafer size of 2 inches (5 cm).

The larger wafer size increases the qubit’s capacity to 25 EB – the equivalent, the researchers say, of a billion single-layer 25GB Blu-Ray discs.

A Kenzan diamond paper – Two-Inch High-Quality Diamond Heteroepitaxial Growth on Sapphire for Power Devices – will be presented at the International Conference on Compound Semiconductor Manufacturing Technology 2022 on May 10. Let’s see if quantum computer builders are impressed enough to use these cakes.