How to make a Physcal identity column in Existing table

CREATE TABLE #Table1
(
Id INT NULL,
Column1 VARCHAR(50)
)
GO
INSERT #Table1(Column1) VALUES('Failover Clustering')
INSERT #Table1(Column1) VALUES('Mirroring')
INSERT #Table1(Column1) VALUES('Replication')
INSERT #Table1(Column1) VALUES('Log Shipping')
INSERT #Table1(Column1) VALUES('Database Snapshot')
INSERT #Table1(Column1) VALUES('Database Backup')
GO

DECLARE @Seq INT

SELECT @Seq = 0

UPDATE #Table1 SET Id = @Seq , @Seq = @Seq + 1

GO
SELECT * FROM #Table1
GO
DROP TABLE #Table1
GO