Incompatibility of classical memory for quantum computing is explained. Efficient storage/modification of quantum or classical data is accomplished by using a quantum random-access memory (QRAM). A QRAM applies the principle of quantum superposition for simultaneously accessing all the data stored in the memory cell to assure the superior performance of quantum algorithms. Data reading and writing in a bucket-brigade QRAM are described and the feasibility of its optical implementation is discussed. Quantum computers are understood through layered architectures, viz., 3-, 4-, and 5-layer architectures. Organization of a superconducting quantum computer is illustrated by considering a generic architecture. The superconducting transmon qubits produced inside a dilution refrigerator are manipulated by sequences of microwave pulses. Electronic systems used for producing the control signals and reading the quantum information are described. Quantum computers have been built by several industry giants. Improved quantum processors are being assembled with continuous advancements and refinements. Future computing is likely to follow a hybrid paradigm in which the quantum computers will work in tandem with classical computers in a seamless, integrated environment. Each type of computing will complement the strengths and weaknesses of its counterpart.
Incompatibility of classical memory for quantum computing is explained. Efficient storage/modification of quantum or classical data is accomplished by using a quantum random-access memory (QRAM). A QRAM applies the principle of quantum superposition for simultaneously accessing all the data stored in the memory cell to assure the superior performance of quantum algorithms. Data reading and writing in a bucket-brigade QRAM are described and the feasibility of its optical implementation is discussed. Quantum computers are understood through layered architectures, viz., 3-, 4-, and 5-layer architectures. Organization of a superconducting quantum computer is illustrated by considering a generic architecture. The superconducting transmon qubits produced inside a dilution refrigerator are manipulated by sequences of microwave pulses. Electronic systems used for producing the control signals and reading the quantum information are described. Quantum computers have been built by several industry giants. Improved quantum processors are being assembled with continuous advancements and refinements. Future computing is likely to follow a hybrid paradigm in which the quantum computers will work in tandem with classical computers in a seamless, integrated environment. Each type of computing will complement the strengths and weaknesses of its counterpart.
Quantum Random Access Memory (QRAM) has the potential to revolutionize the area of quantum computing. QRAM uses quantum computing principles to store and modify quantum or classical data efficiently, greatly accelerating a wide range of computer processes. Despite its importance, there is a lack of comprehensive surveys that cover the entire spectrum of QRAM architectures. We fill this gap by providing a comprehensive review of QRAM, emphasizing its significance and viability in existing noisy quantum computers. By drawing comparisons with conventional RAM for ease of understanding, this survey clarifies the fundamental ideas and actions of QRAM. QRAM provides an exponential time advantage compared to its classical counterpart by reading and writing all data at once, which is achieved owing to storage of data in a superposition of states. Overall, we compare six different QRAM technologies in terms of their structure and workings, circuit width and depth, unique qualities, practical implementation, and drawbacks. In general, with the exception of trainable machine learning-based QRAMs, we observe that QRAM has exponential depth/width requirements in terms of the number of qubits/qudits and that most QRAM implementations are practical for superconducting and trapped-ion qubit systems.
Memory is an indispensable component in classical computing systems. While the development of quantum computing is still in its early stages, current quantum processing units mainly function as quantum registers. Consequently, the actual role of quantum memory in future advanced quantum computing architectures remains unclear. With the rapid scaling of qubits, it is opportune to explore the potential and feasibility of quantum memory across different substrate device technologies and application scenarios. In this paper, we provide a full design stack view of quantum memory. We start from the elementary component of a quantum memory device, quantum memory cells. We provide an abstraction to a quantum memory cell and define metrics to measure the performance of physical platforms. Combined with addressing functionality, we then review two types of quantum memory devices: random access quantum memory (RAQM) and quantum random access memory (QRAM). Building on top of these devices, quantum memory units in the computing architecture, including building a quantum memory unit, quantum cache, quantum buffer, and using QRAM for the quantum input-output module, are discussed. We further propose the programming model for the quantum memory units and discuss their possible applications. By presenting this work, we aim to attract more researchers from both the Quantum Information Science (QIS) and classical memory communities to enter this emerging and exciting area.
Operating on the principles of quantum mechanics, quantum algorithms hold the promise for solving problems that are beyond the reach of the best-available classical algorithms. An integral part of realizing such speedup is the implementation of quantum queries, which read data into forms that quantum computers can process. Quantum random access memory (QRAM) is a promising architecture for realizing quantum queries. However, implementing QRAM in practice poses significant challenges, including query latency, memory capacity and fault-tolerance.
A random access memory, or RAM, is a device that, when interrogated, returns the content of a memory location in a memory array. A quantum RAM, or qRAM, allows one to access superpositions of memory sites, which may contain either quantum or classical information. RAMs and qRAMs with n-bit addresses can access 2n memory sites. Any design for a RAM or qRAM then requires O(2n) two-bit logic gates. At first sight this requirement might seem to make large scale quantum versions of such devices impractical, due to the difficulty of constructing and operating coherent devices with large numbers of quantum logic gates. Here we analyze two different RAM architectures (the conventional fanout and the ``bucket brigade'') and propose some proof-of-principle implementations, which show that, in principle, only O(n) two-qubit physical interactions need take place during each qRAM call. That is, although a qRAM needs O(2n) quantum logic gates, only O(n) need to be activated during a memory call. The resulting decrease in resources could give rise to the construction of large qRAMs that could operate without the need for extensive quantum error correction.
Owing to the significant progress in manufacturing desktop quantum computers, the quest to achieve efficient quantum random access memory (QRAM) became inevitable. In this paper, we propose a novel efficient random access memory for quantum computers. The proposed QRAM has a fixed structure and can be used efficiently to store both known and unknown classical/quantum data. The storage capacity of the proposed QRAM is more efficient than that of the classical RAMs and can be used to store both classical and quantum information. Furthermore, the proposed model can access an arbitrary location in O(1) compared with other state-of-the-art models.
Quantum memory is proposed as an analogue to classical computer memory, like the random-access memory (RAM). RAM is a form of computer memory that can be read and changed in any order, typically used to store working data. In quantum machine learning domain, the usage of quantum random access memory (qRAM) is proposed to avoid input destruction problem. The method of qRAM is related to the entanglement of the index qubits that are in the superposition with the patterns. The method of qRAM is related to the entanglement of the index qubits that are in the superposition with the patterns. As in the method of the entanglement of the index qubits, the qubits of qRAM are entangled during the reading operation and have to be un-computed after computation.