I lost a private key for an ethereum wallet. While seeking for information I found out that only quantum computers can decrypt a public key. Is this really a possibility? Thanks in advance.
Welcome to QCSE! Sorry, but it's not possible. Quantum computers are not yet powerful enough to assist in any meaningful decryption. Currently available quantum chips, which are generally less than 100 qubits, are many orders of magnitude to small for this task.
There are several other more technical reasons that this is impossible with the current state of technology as well. If it were possible, any system relying on ECDSA would be vulnerable fraudulent signatures.
However, most wallets have a backup phrase to allow an owner to recover lost private keys. That would be a much more productive route to pursue than trying to break ECDSA with today's quantum computers.