In quantum computing, a quantum memory is the quantum-mechanical version of ordinary computer memory. Whereas ordinary memory stores information as binary states (represented by "1"s and "0"s), quantum memory stores a quantum state for later retrieval. These states hold useful computational information known as qubits. Unlike the classical memory of everyday computers, the states stored in quantum memory can be in a quantum superposition, giving much more practical flexibility in quantum algorithms than classical information storage. Quantum memory is essential for the development of many devices in quantum information processing, including a synchronization tool that can match the various processes in a quantum computer, a quantum gate that maintains the identity of any state, and a mechanism for converting predetermined photons into on-demand photons. Quantum memory can be used in many aspects, such as quantum computing and quantum communication. Continuous research and experiments have enabled quantum memory to realize the storage of qubits.
Background and history The interaction of quantum radiation with multiple particles has sparked scientific interest over the past decade. Quantum memory is one such field, mapping the quantum state of light onto a group of atoms and then restoring it to its original shape. Quantum memory is a key element in information processing, such as optical quantum computing and quantum communication, while opening a new way for the foundation of light-atom interaction. Restoring the quantum state of light remains a challenge for the field. Quantum memory based on the quantum exchange to store photon qubits has been demonstrated to be possible. Kessel and Moiseev discussed quantum storage in the single photon state in 1993. The experiment was analyzed in 1998 and demonstrated in 2003. In summary, the study of quantum storage in the single photon state can be regarded as the product of the classical optical data storage technology proposed in 1979 and 1982, an idea inspired by the high density of data storage in the mid-1970s. Optical data storage can be achieved by using absorbers to absorb different frequencies of light, which are then directed to beam space points and stored.
Types
Atomic gases Normal, classical optical signals are transmitted by varying the amplitude of light. In this case, a piece of paper, or a computer hard disk, can be used to store information on the lamp. In the quantum information scenario, however, the information may be encoded according to the amplitude and phase of the light. For some signals, you cannot measure both the amplitude and phase of the light without interfering with the signal. To store quantum information, light itself needs to be stored without being measured. An atomic gas quantum memory is recording the state of light into the atomic cloud. When light's information is stored by atoms, relative amplitude and phase of light is mapped to atoms and can be retrieved on-demand.
Solid state In classical computing, memory is a trivial resource that can be replicated in long-lived memory hardware and retrieved later for further processing. In quantum computing, this is forbidden because, according to the no clone theorem, any quantum state cannot be reproduced completely. Therefore, in the absence of quantum error correction, the storage of qubits is limited by the internal coherence time of the physical qubits holding the information. "Quantum memory" beyond the given physical qubit storage limits will be a quantum information transmission to "storing qubits" not easily affected by environmental noise and other factors. The information would later be transferred back to the preferred "process qubits" to allow rapid operations or reads.
Discovery Optical quantum memory is usually used to detect and store single photon quantum states. However, producing efficient memory of this kind is still a huge challenge for current science. A single photon is so low in energy as to be lost in a complex light background. These problems have long kept quantum storage rates below 50%. A team led by professor Du Shengwang of the department of physics at the Hong Kong University of science and technology and William Mong Institute of Nano Science and Technology at HKUST has found a way to increase the efficiency of optical quantum memory to more than 85 percent. The discovery also brings the popularity of quantum computers closer to reality. At the same time, the quantum memory can also be used as a repeater in the quantum network, which lays the foundation for the quantum Internet.
Research and application Quantum memory is an important component of quantum information processing applications such as quantum network, quantum repeater, linear optical quantum computation or long-distance quantum communication. Optical data storage has been an important research topic for many years. Its most interesting function is the use of the laws of quantum physics to protect data from theft, through quantum computing and quantum cryptography unconditionally guaranteed communication security. They allow particles to be superimposed and in a superposition state, which means they can represent multiple combinations at the same time. These particles are called quantum bits, or qubits. From a cybersecurity perspective, the magic of qubits is that if a hacker tries to observe them in transit, their fragile quantum states shatter. This means it is impossible for hackers to tamper with network data without leaving a trace. Now, many companies are taking advantage of this feature to create networks that transmit highly sensitive data. In theory, these networks are secure.
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