The realm of quantum computing continues to amaze with its potential for solving complex problems at lightning speed. One such problem, navigating through mathematical mazes, has always presented a unique challenge. Quantum researchers developed an algorithm two decades ago that allowed for faster maze traversal compared to classical algorithms. However, there was a catch—the quantum algorithm lacked the ability to remember the path it took.
This tradeoff between speed and memory retention has intrigued scientists for years. Is it possible to find the exit quickly while still retaining the knowledge of the path taken? Recent research conducted by Matthew Coudron and his team at the National Institute of Standards and Technology shows that in a broad class of fast quantum algorithms, it is impossible to find the path without temporarily losing track of the entrance. Forgetting, it seems, is an inevitable necessity in quantum mazesolving.
The power of quantum computers lies in their ability to simultaneously explore multiple options, thanks to a phenomenon called superposition. While classical computers must consider each option individually, quantum computers can check multiple possibilities simultaneously. However, the result of a superposition of choices doesn’t reveal a superposition of outcomes. Instead, it provides a single outcome with a unique probability. Quantum algorithms take advantage of interference between these probabilities to increase the likelihood of obtaining the desired answer while diminishing the chances of other outcomes.
Not all computational tasks can benefit from a quantum speedup, and researchers are still working to determine where quantum algorithms excel. Peter Shor’s breakthrough in 1994 introduced a quantum algorithm capable of factoring large numbers—a task that classical computers struggle with. Lov Grover continued this trend in 1996 with his quantum search algorithm, which solved a generic search problem more efficiently than classical algorithms. These early successes demonstrated the potential gulf between classical and quantum computing capabilities.
The exploration of graph theory has provided valuable insights into the limitations and possibilities of quantum algorithms. Search problems can be framed as graphs, with nodes representing starting and destination points and edges representing possible choices at each step. Grover’s search problem, for example, corresponds to a graph where every node is connected to every other node. Classical algorithms explore these graphs one node at a time, while quantum algorithms can simultaneously traverse multiple edges through superposition.
In 2002, computer scientists identified a classically intractable search problem that could be easily solved by a quantum algorithm. This problem involved a special type of graph called a welded tree graph. By combining two identical trees and connecting their leaves using a random process, scientists created a mazelike structure that posed a difficult search challenge. Quantum algorithms proved capable of navigating through this maze at an exceptional speed.
While the new findings by Coudron and his team may seem disheartening, they provide a better understanding of the limitations and possibilities of quantum mazesolving. Quantum computers continue to push the boundaries of what is possible, but they also require new approaches and strategies to harness their power effectively.
Frequently Asked Questions:

Can quantum computers solve mazes faster than classical computers?
Yes, quantum algorithms can provide faster solutions to certain types of mazes, thanks to their ability to explore multiple possibilities simultaneously. 
Do quantum algorithms remember the path they took in mazes?
No, one drawback of fast quantum algorithms is that they cannot retain the memory of the path taken. They find the exit quickly but have no recollection of how they got there. 
What is superposition in quantum computing?
Superposition is a phenomenon that allows quantum computers to exist in multiple states simultaneously. It enables them to explore multiple solutions to a problem in parallel, leading to potential speedups.
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