IBM Quantum and IonQ researchers have developed a classical simulation algorithm that can compute quantum computations faster than previously reported. The team simulated Instantaneous Quantum Polynomial-Time (IQP) computations, a type of quantum computation, for up to 96 qubits, taking an average of 4.16629 seconds to compute a single amplitude. The researchers believe that their algorithm can simulate larger quantum computations using classical hardware, challenging the notion that quantum computations are too complex to be reproduced by classical means.
Quantum Computing: Classical Simulation of Quantum Circuits
Quantum computing is a rapidly advancing field, with the potential to outperform classical computing in certain tasks. However, a recent study by researchers from IBM Quantum and IonQ has challenged the notion of quantum advantage, demonstrating a classical simulation algorithm that can efficiently simulate certain quantum circuits. The study was led by Dmitri Maslov and Sergey Bravyi from IBM, and Felix Tripier, Andrii Maksymov, and Joe Latone from IonQ.
Quantum Advantage and IQP Circuits
Quantum advantage refers to the point at which a quantum computer can perform a task that is infeasibly complex for a classical computer. A recent publication introduced a type of Instantaneous Quantum Polynomial-Time (IQP) computation, which was demonstrated using a 48-qubit quantum hardware. The authors of that study suggested that simulating such circuits would be challenging and time-consuming for classical computers. However, the IBM and IonQ researchers have developed a classical simulation algorithm that can compute an amplitude for the 48-qubit computation in just 0.00257947 seconds, significantly faster than the original authors’ projections.
Classical Simulation of Quantum Circuits
The researchers’ classical simulation algorithm is not significantly affected by the addition of CNOT layers, a factor that was previously thought to increase the complexity of the simulation. The team was able to simulate IQP computations for up to 96 qubits, taking an average of 4.16629 seconds to compute a single amplitude. They estimated that a 192-qubit simulation should be feasible for computations relying on Tensor Processing Units.
Types of Quantum Computation Simulation
The researchers distinguish between two types of quantum computation simulation: ‘weak’ or ‘direct’ simulation, which allows sampling bitstrings computed by a given quantum circuit, and ‘strong’ simulation, which computes the entire amplitude for a given desired observable. The team’s focus was on ‘strong’ simulation, and they developed an algorithm that can compute the entire amplitude of a specific quantum circuit in a fraction of a second.
Modifying Quantum Circuits
The researchers also explored various modifications to the quantum circuits that could potentially increase the difficulty of classical simulation. However, they found that adding or removing certain gates, increasing the computation depth, or increasing the number of qubits did not significantly affect the complexity of the classical simulation. They concluded that a more fruitful direction for demonstrating quantum advantage might be the development of a complete logical library and full-fledged fault tolerance, rather than simply increasing the number of qubits.
